<!doctypehtml SYSTEM "about:legacy-compat"><html lang=en-us xml:lang=en-us xmlns=http://www.w3.org/1999/xhtml xmlns:whc=http://www.oxygenxml.com/webhelp/components><meta content="text/html; charset=utf-8"http-equiv=Content-Type><link rel="shortcut icon"href=../../favicon.ico><link href=../../favicon.ico rel=icon><meta content="Transport Layer Security (TLS) in the Email Appliance Transport Layer Security (TLS) enables the encrypted communication of messages between hosts that support TLS and can also allow one host to ..."name=description><meta content="(C) Copyright 2018"name=copyright><meta content="(C) Copyright 2018"name=DC.rights.owner><meta content=reference name=DC.Type><meta content="Transport Layer Security (TLS) Email Encryption"name=DC.Title><meta content=../tasks/ConfigPolEncryptOn.html name=DC.Relation scheme=URI><meta content=../tasks/ConfigPolEncryptDomains.html name=DC.Relation scheme=URI><meta content=../tasks/ConfigPolEncryptDelete.html name=DC.Relation scheme=URI><meta content=../concepts/ConfigPolEncryption.html name=DC.Relation scheme=URI><meta content=certificates.html name=DC.Relation scheme=URI><meta content=../concepts/ConfigSysCertificates.html name=DC.Relation scheme=URI><meta content=csr_request.html name=DC.Relation scheme=URI><meta content="Sophos Email Appliance"name=prodname><meta content=4.3 name=version><meta content=XHTML name=DC.Format><meta content=tls_encryption name=DC.Identifier><meta content=en-us name=DC.Language><title>
   Transport Layer Security (TLS) Email Encryption
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wh_toggle_button"data-target=.wh_top_menu_and_indexterms_link data-toggle=collapse type=button><span class=icon-bar> </span> <span class=icon-bar> </span> <span class=icon-bar> </span></button><form action=../../user_guide.pdf class=sophos_button onclick=this.target='_blank'><button class="navbar-toggle collapsed wh_toggle_button button_text">PDF</button></form></div><div class="wh_top_menu_and_indexterms_link collapse navbar-collapse"><div class=wh_top_menu><ul><li class=has-children><span class=topicref> <a data-id=AboutYourES1000 href=../../sea/concepts/AboutYourES4000.html> About Your Email Appliance </a> </span> <ul><li><span class=topicref> <a data-id=ES1000Features href=../../sea/concepts/ES4000Features.html> Email Appliance Features </a> </span><li><span class=topicref> <a data-id=ES4000UserInterface href=../../sea/concepts/ES4000UserInterface.html> The Email Appliance User Interface </a> </span><li><span class=topicref> <a data-id=ConfigMonitoring href=../../sea/concepts/ConfigMonitoring.html> Sophos Proactive Monitoring </a> </span><li class=has-children><span class=topicref> <a data-id=GettingSupport href=../../sea/concepts/GettingSupport.html> Getting Support </a> </span> <ul><li><span class=topicref> <a data-id=HardwareSupport href=../../sea/concepts/HardwareSupport.html> Hardware Support </a> </span></ul></ul><li class=has-children><span class=topicref> <a data-id=GettingStarted href=../../sea/concepts/GettingStarted.html> Getting Started </a> </span> <ul><li class=has-children><span class=topicref> <a data-id=MailRouting href=../../sea/concepts/GSMailRouting.html> Mail Routing </a> </span> <ul><li><span class=topicref> <a data-id=SimpleRouting href=../../sea/concepts/GSSimpleRouting.html> Simple Mail Routing </a> </span><li><span class=topicref> <a data-id=ComplexRouting href=../../sea/concepts/GSComplexRouting.html> More Complex Mail Routing </a> </span></ul><li><span class=topicref> <a data-id=GSPolicy href=../../sea/concepts/GSPolicy.html> Policy </a> </span><li><span class=topicref> <a data-id=GSQuarantine href=../../sea/concepts/GSQuarantine.html> Quarantine </a> </span><li><span class=topicref> <a data-id=GSAccounts href=../../sea/concepts/GSAccounts.html> Administrator and User Accounts </a> </span><li><span class=topicref> <a data-id=GSUpdates href=../../sea/concepts/GSUpdates.html> Email Appliance Updates </a> </span><li><span class=topicref> <a data-id=ConfigSysCluster href=../../sea/tasks/ConfigSysCluster.html> Clustering </a> </span></ul><li class=has-children><span class=topicref> <a data-id=ES1000Hardware href=../../sea/concepts/ES4000Hardware.html> Email Appliance Hardware </a> </span> <ul><li class=has-children><span class=topicref> <a data-id=HardwareTroubleshooting href=../../sea/concepts/HardwareTroubleshooting.html> Hardware Troubleshooting </a> </span> <ul><li><span class=topicref> <a data-id=HardwareAlarms href=../../sea/concepts/HardwareAlarms.html> Audible Alarms [ES4000/5000/8000 Only] </a> </span><li><span class=topicref> <a data-id=HardwareAlerts href=../../sea/concepts/HardwareAlerts.html> Hardware Alerts </a> </span></ul><li><span class=topicref> <a data-id=HardwareHardDriveFRU href=../../sea/concepts/Hardware5000HardDriveFRU.html> Replacing an ES5000/8000 Hard Drive </a> </span><li><span class=topicref> <a data-id=Hardware5000PowerSupplyFRU href=../../sea/concepts/Hardware5000PowerSupplyFRU.html> Replacing an ES5000/8000 Power Supply </a> </span><li><span class=topicref> <a data-id=HardwareHardDriveFRU href=../../sea/concepts/HardwareHardDriveFRU.html> Replacing an ES4000 Hard Drive </a> </span><li><span class=topicref> <a data-id=HardwarePowerSupplyFRU href=../../sea/concepts/HardwarePowerSupplyFRU.html> Replacing an ES4000 Power Supply </a> </span></ul><li><span class=topicref> <a data-id=Dashboard href=../../sea/concepts/Dashboard.html> Dashboard </a> </span><li class=has-children><span class=topicref> <a data-id=Configuration href=../../sea/concepts/Configuration.html> Configuration </a> </span> <ul><li class=has-children><span class=topicref> <a data-id=ConfigAccounts href=../../sea/concepts/ConfigAccounts.html> Accounts </a> </span> <ul><li><span class=topicref> <a data-id=ConfigAccntsAdmin href=../../sea/concepts/ConfigAccntsAdmin.html> Administrators </a> </span><li><span class=topicref> <a data-id=ConfigAccntsUsrGroups href=../../sea/concepts/ConfigAccntsUsrGroups.html> User Groups </a> </span><li><span class=topicref> <a data-id=ConfigAccntsUsrPrefs href=../../sea/concepts/ConfigAccntsUsrPrefs.html> User Preferences </a> </span></ul><li class=has-children><span class=topicref> <a data-id=ConfigPolicy href=../../sea/concepts/ConfigPolicy.html> Policy </a> </span> <ul><li><span class=topicref> <a data-id=policy_flow href=../../sea/references/policy_flow.html> Policy Message Flow </a> </span><li><span class=topicref> <a data-id=ConfigPolAntiVirusRef href=../../sea/references/ConfigPolAntiVirusRef.html> Threat Protection </a> </span><li><span class=topicref> <a data-id=ConfigPolAntiSpamRef href=../../sea/references/ConfigPolAntiSpamRef.html> Anti-Spam </a> </span><li><span class=topicref> <a data-id=search href=../../sea/references/DataControlRef.html> Data Control </a> </span><li><span class=topicref> <a data-id=ConfigPolContentRef href=../../sea/references/ConfigPolContentRef.html> Additional Policy </a> </span><li><span class=topicref> <a data-id=ConfigPolAllowBlockLists href=../../sea/tasks/ConfigPolAllowBlockLists.html> Allow/Block Lists </a> </span><li><span class=topicref> <a data-id=configPolFilteringOptions href=../../sea/concepts/ConfigPolFilteringOptions.html> Filtering Options </a> </span><li><span class=topicref> <a data-id=concept_egs_hb1_p5 href=../../sea/concepts/ConfigPolSandstorm.html> Sandstorm </a> </span><li><span class=topicref> <a data-id=ConfigPolEncryption href=../../sea/concepts/ConfigPolEncryption.html> Encryption </a> </span><li><span class=topicref> <a data-id=ConfigPolSMTP_Auth href=../../sea/tasks/ConfigPolSMTP_Auth.html> SMTP Authentication </a> </span><li><span class=topicref> <a data-id=ConfigPolSMTP_Opts href=../../sea/concepts/ConfigPolSMTP_Opts.html> SMTP Options </a> </span></ul><li class=has-children><span class=topicref> <a data-id=ConfigSystem href=../../sea/concepts/ConfigSystem.html> System </a> </span> <ul><li><span class=topicref> <a data-id=ConfigSysUpdate href=../../sea/concepts/ConfigSysUpdate.html> Updates </a> </span><li><span class=topicref> <a data-id=ConfigSysAlerts href=../../sea/concepts/ConfigSysAlerts.html> Alerts & Monitoring </a> </span><li><span class=topicref> <a data-id=ConfigSysBackup href=../../sea/tasks/ConfigSysBackup.html> Backup </a> </span><li><span class=topicref> <a data-id=ConfigSysDirectoryServices href=../../sea/concepts/ConfigSysDirectoryServices.html> Directory Services </a> </span><li><span class=topicref> <a data-id=ConfigSysCertificates href=../../sea/concepts/ConfigSysCertificates.html> Certificates </a> </span><li><span class=topicref> <a data-id=ConfigSysCluster href=../../sea/tasks/ConfigSysCluster-1.html> Clustering </a> </span><li><span class=topicref> <a data-id=ConfigSysTimeZone href=../../sea/tasks/ConfigSysTimeZone.html> Time Zone </a> </span><li><span class=topicref> <a data-id=ConfigSysConfigSync href=../../sea/concepts/SCPSyncOverview.html> Configuration Sync </a> </span></ul><li class=has-children><span class=topicref> <a data-id=ConfigMailRouting href=../../sea/concepts/ConfigMailRouting.html> Routing </a> </span> <ul><li><span class=topicref> <a data-id=ConfigRoutingDeliveryServers href=../../sea/tasks/ConfigRoutingDeliveryServers.html> Adding/Removing Mail Delivery Servers </a> </span><li><span class=topicref> <a data-id=ConfigRoutingMailDomains href=../../sea/tasks/ConfigRoutingMailDomains.html> Adding/Removing Mail Domains </a> </span><li><span class=topicref> <a data-id=ConfigRoutingInternalMailHosts href=../../sea/concepts/ConfigRoutingInternalMailHosts.html> Internal Mail Hosts </a> </span><li><span class=topicref> <a data-id=ConfigRoutingOutboundMailProxy href=../../sea/tasks/ConfigRoutingOutboundMailProxy.html> Setting an Outbound Mail Proxy </a> </span><li><span class=topicref> <a data-id=ConfigRoutingTrustedRelays href=../../sea/tasks/ConfigRoutingTrustedRelays.html> Adding/Removing Trusted Relays </a> </span><li><span class=topicref> <a data-id=ConfigRoutingAddressRewrite href=../../sea/concepts/ConfigRoutingAddressRewriteAbout.html> About Address Rewriting </a> </span></ul><li class=has-children><span class=topicref> <a data-id=ConfigNetwork href=../../sea/concepts/ConfigNetwork.html> Network </a> </span> <ul><li><span class=topicref> <a data-id=ConfigNetInterfaceSettings href=../../sea/tasks/ConfigNetInterfaceSettings.html> Configuring Interface Settings </a> </span><li><span class=topicref> <a data-id=ConfigNetHostnameProxy href=../../sea/tasks/ConfigNetHostnameProxy.html> Setting a Hostname and Proxy </a> </span><li><span class=topicref> <a data-id=ConfigNetNetworkConnectivity href=../../sea/tasks/ConfigNetNetworkConnectivity.html> Testing Network Connectivity </a> </span></ul></ul><li class=has-children><span class=topicref> <a data-id=Reports href=../../sea/concepts/Reports.html> Reports </a> </span> <ul><li><span class=topicref> <a data-id=ReportCategories href=../../sea/concepts/ReportCategories.html> Report Categories </a> </span><li><span class=topicref> <a data-id=ReportGenerating href=../../sea/tasks/ReportGenerating.html> Creating and Running Reports </a> </span><li><span class=topicref> <a data-id=ReportPrinting href=../../sea/tasks/ReportPrinting.html> Printing Reports </a> </span><li><span class=topicref> <a data-id=ReportExporting href=../../sea/tasks/ReportExporting.html> Exporting Reports </a> </span><li><span class=topicref> <a data-id=ReportTrustedRelays href=../../sea/tasks/ReportTrustedRelays.html> Adding Trusted Relays from a Report </a> </span></ul><li class=has-children><span class=topicref> <a data-id=search href=../../sea/concepts/Search.html> Search </a> </span> <ul><li class=has-children><span class=topicref> <a data-id=SearchTheQuarantine href=../../sea/concepts/SearchTheQuarantine.html> Quarantine Search </a> </span> <ul><li><span class=topicref> <a data-id=SearchTheQuarantineSearch href=../../sea/tasks/SearchTheQuarantineSearch.html> Searching the Quarantine </a> </span><li><span class=topicref> <a data-id=SearchTheQuarantineViewRslts href=../../sea/tasks/SearchTheQuarantineViewRslts.html> Viewing Quarantine Search Results </a> </span><li><span class=topicref> <a data-id=SearchTheQuarantineMng href=../../sea/tasks/SearchTheQuarantineMng.html> Managing Quarantined Messages </a> </span></ul><li class=has-children><span class=topicref> <a data-id=SearchTheLogs href=../../sea/concepts/SearchTheLogs.html> Logs Search </a> </span> <ul><li><span class=topicref> <a data-id=SearchTheLogsSearch href=../../sea/tasks/SearchTheLogsSearch.html> Searching the Mail Logs </a> </span><li><span class=topicref> <a data-id=SearchTheLogsViewRslts href=../../sea/tasks/SearchTheLogsViewRslts.html> Viewing Logs Search Results </a> </span><li><span class=topicref> <a data-id=SearchTheLogsAnalyze href=../../sea/tasks/SearchTheLogsAnalyze.html> Analyzing Message Logs </a> </span></ul><li class=has-children><span class=topicref> <a data-id=SearchTheMailQueues href=../../sea/concepts/SearchTheMailQueues.html> Mail Queues Search </a> </span> <ul><li><span class=topicref> <a data-id=SearchTheMailQueuesSearch href=../../sea/tasks/SearchTheMailQueuesSearch.html> Searching the Mail Queues </a> </span><li><span class=topicref> <a data-id=SearchTheMailQueuesViewRslts href=../../sea/tasks/SearchTheMailQueuesViewRslts.html> Viewing Mail Queues Search Results </a> </span><li><span class=topicref> <a data-id=SearchTheMailQueuesDel href=../../sea/tasks/SearchTheMailQueuesDel.html> Deleting Queued Messages </a> </span><li><span class=topicref> <a data-id=SearchTheMailQueuesRelease href=../../sea/tasks/SearchTheMailQueuesRelease.html> Releasing or Rescanning Queued Messages </a> </span></ul></ul><li class=has-children><span class=topicref> <a data-id=SystemStatus href=../../sea/concepts/SystemStatus.html> System Status </a> </span> <ul><li><span class=topicref> <a data-id=SystemStatusMailFlow href=../../sea/concepts/SystemStatusMailFlow.html> Mail Flow </a> </span><li><span class=topicref> <a data-id=SystemStatusQuarantine href=../../sea/concepts/SystemStatusQuarantine.html> Quarantine </a> </span><li><span class=topicref> <a data-id=SystemStatusSoftware href=../../sea/concepts/SystemStatusSoftware.html> Software </a> </span><li><span class=topicref> <a data-id=SystemStatusHardware href=../../sea/concepts/SystemStatusHardware.html> Hardware </a> </span><li><span class=topicref> <a data-id=SystemStatusLicense href=../../sea/concepts/SystemStatusLicense.html> License </a> </span></ul><li class=has-children><span class=topicref> <a data-id=HelpUsing href=../../sea/concepts/HelpUsing.html> Using Help </a> </span> <ul><li><span class=topicref> <a data-id=HelpSearch href=../../sea/tasks/HelpSearch.html> Searching the Documentation </a> </span></ul><li class=has-children><span class=topicref> <a data-id=Intro href=../../sea/concepts/Wiz_Introduction.html> Setup and Configuration Guide </a> </span> <ul><li class=has-children><span class=topicref> <a data-id=Init_Config href=../../sea/concepts/Wiz_Initial_Config.html> Initial Configuration </a> </span> <ul><li><span class=topicref> <a data-id=Activate href=../../sea/tasks/Wiz_Activation.html> Activating the Email Appliance </a> </span><li><span class=topicref> <a data-id=NetInterface href=../../sea/tasks/Wiz_Network_Interface.html> Network Interface </a> </span><li><span class=topicref> <a data-id=Hostname_Proxy href=../../sea/tasks/Wiz_Host_Proxy.html> Hostname and Proxy </a> </span><li><span class=topicref> <a data-id=Netwk_Connect href=../../sea/tasks/Wiz_Netwk_Connect.html> Network Connectivity </a> </span><li><span class=topicref> <a data-id=Reg_Update href=../../sea/tasks/Wiz_Reg_Update.html> Register and Update </a> </span><li><span class=topicref> <a data-id=Clustering href=../../sea/tasks/Wiz_Failover.html> Clustering </a> </span><li><span class=topicref> <a data-id=TimeZone href=../../sea/tasks/Wiz_Time_Zone.html> Time Zone </a> </span><li><span class=topicref> <a data-id=Mail_Del_Servers href=../../sea/tasks/Wiz_Mail_Del_Servers.html> Mail Delivery Servers </a> </span><li><span class=topicref> <a data-id=Inc_Mail_Domains href=../../sea/tasks/Wiz_Inc_Mail_Domains.html> Incoming Mail Domains </a> </span><li><span class=topicref> <a data-id=Mail_Relays href=../../sea/tasks/Wiz_Mail_Relays.html> Internal Mail Hosts </a> </span><li><span class=topicref> <a data-id=Anti_Virus href=../../sea/tasks/Wiz_Anti_Virus.html> Anti-Virus Settings </a> </span><li><span class=topicref> <a data-id=Anti_Spam href=../../sea/tasks/Wiz_Anti_Spam.html> Anti-Spam Settings </a> </span><li><span class=topicref> <a data-id=Not_Addresses href=../../sea/tasks/Wiz_Not_Addresses.html> Appliance Alerting </a> </span><li><span class=topicref> <a data-id=Contact_Support href=../../sea/tasks/Wiz_Contact_Support.html> Appliance Support Contact </a> </span><li><span class=topicref> <a data-id=Summary href=../../sea/tasks/Wiz_Summary.html> Summary </a> </span></ul><li class=has-children><span class=topicref> <a data-id=Post_Install href=../../sea/concepts/Wiz_Post_Install.html> Post-Installation Configuration/Integration </a> </span> <ul><li><span class=topicref> <a data-id=Wiz_Test_Msgs href=../../sea/concepts/Wiz_Test_Msgs.html> Testing Appliance Mail Flow </a> </span><li><span class=topicref> <a data-id=Wiz_Active_Dir href=../../sea/tasks/Wiz_Active_Directory.html> Configuring Directory Services </a> </span><li><span class=topicref> <a data-id=Wiz_User_Prefs href=../../sea/tasks/Wiz_User_Prefs.html> Configuring User Preferences </a> </span><li><span class=topicref> <a data-id=Wiz_Out_Mail_Proxy href=../../sea/tasks/Wiz_Out_Mail_Proxy.html> Configuring Internal Mail Hosts/Outbound Mail Proxy </a> </span><li><span class=topicref> <a data-id=Wiz_Trusted_Relay href=../../sea/tasks/Wiz_Trusted_Relays.html> Configuring Trusted Relays </a> </span></ul></ul><li><span class=topicref> <a data-id=PortConfig href=../../sea/concepts/PortConfig.html> Configuring Ports </a> </span><li><span class=topicref> <a data-id=browser_support href=../../sea/references/browser_support.html> Supported Browsers </a> </span><li><span class=topicref> <a data-id=spx_api href=../../sea/references/spx_api.html> Creating a Custom Web Service for SPX </a> </span><li><span class=topicref> <a data-id=PolAboutActionsTempVars href=../../sea/concepts/PolAboutActionsTempVars.html> Template Variables </a> </span><li><span class=topicref> <a data-id=DBTempVarsConflict href=../../sea/concepts/TempVarsConflict.html> Password Option/Template Variable Mismatches </a> </span><li class=has-children><span class=topicref> <a data-id=DialogBoxHelp href=../../sea/concepts/DialogBoxHelp.html> Dialog Box Help </a> </span> <ul><li><span class=topicref> <a data-id=DBActiveDirectory href=../../sea/tasks/DBActiveDirectory.html> Directory Services Groups </a> </span><li><span class=topicref> <a data-id=DBAddCertAuthorities href=../../sea/tasks/DBAddCertAuthorities-1.html> Add Certificate Authorities </a> </span><li><span class=topicref> <a data-id=DBImportCert href=../../sea/tasks/DBImportCert.html> Complete CSR </a> </span><li><span class=topicref> <a data-id=DBAddUser href=../../sea/tasks/DBAddUser.html> Add User or Modify User </a> </span><li><span class=topicref> <a data-id=DBAddMsgAttr href=../../sea/tasks/DBAddMsgAttr.html> Add Message Attribute </a> </span><li><span class=topicref> <a data-id=DBAdvSysUpdate href=../../sea/tasks/DBAdvSysUpdate.html> Advanced System Updates </a> </span><li><span class=topicref> <a data-id=DBAliasMapEditor href=../../sea/tasks/DBAliasMapEditor.html> Alias Map Editor </a> </span><li><span class=topicref> <a data-id=DBAlertContacts href=../../sea/tasks/DBAlertContacts.html> Alert Contacts </a> </span><li><span class=topicref> <a data-id=DBApplianceSupportContact href=../../sea/tasks/DBApplianceSupportContact.html> Appliance Support Contact </a> </span><li><span class=topicref> <a data-id=DBBannerEditor href=../../sea/tasks/DBBannerEditor.html> Additional Message Actions </a> </span><li><span class=topicref> <a data-id=ConfigPolContent href=../../sea/tasks/ConfigPolContent.html> Additional Policy Example </a> </span><li><span class=topicref> <a data-id=DBBackupsAdv href=../../sea/tasks/DBBackupsAdv.html> Advanced Backup Schedule </a> </span><li><span class=topicref> <a data-id=DBCalendar href=../../sea/tasks/DBCalendar.html> Calendar </a> </span><li><span class=topicref> <a href=../../sea/tasks/DBCertDetails.html> Certificate Details </a> </span><li><span class=topicref> <a data-id=DBCSRDetails href=../../sea/tasks/DBCSRDetails.html> Upload Certificate </a> </span><li><span class=topicref> <a href=../../sea/tasks/DBEditNotifyEmail.html> Edit notification email </a> </span><li><span class=topicref> <a href=../../sea/tasks/DBEditRecipientInstructions.html> Edit SPX Recipient Instructions </a> </span><li><span class=topicref> <a data-id=DBEmailPasswordList href=../../sea/tasks/DBEmailPasswordList.html> Email Password List </a> </span><li><span class=topicref> <a data-id=DBEUWIPorts href=../../sea/tasks/DBEUWIPorts.html> Configure End User Web Quarantine Ports </a> </span><li><span class=topicref> <a data-id=DBForward href=../../sea/tasks/DBForward.html> Forward </a> </span><li><span class=topicref> <a data-id=DBGroupEditor href=../../sea/tasks/DBGroupEditor.html> Group Editor </a> </span><li><span class=topicref> <a data-id=DBGlobalFuncHist href=../../sea/tasks/DBGlobalFuncHist.html> Global Function History </a> </span><li><span class=topicref> <a data-id=DBHeadFootImageUpload href=../../sea/tasks/DBHeadFootImageUpload.html> Upload a Header/Footer Image for the SPX Portal </a> </span><li><span class=topicref> <a data-id=DBIPRouting href=../../sea/tasks/DBIPRouting.html> Additional Network Routes </a> </span><li><span class=topicref> <a data-id=DBListEditor href=../../sea/tasks/DBListEditor.html> List Editor </a> </span><li><span class=topicref> <a data-id=DBListSelector href=../../sea/tasks/DBListSelector.html> List Selector </a> </span><li><span class=topicref> <a data-id=DBListUpload href=../../sea/tasks/DBListUpload.html> Upload </a> </span><li><span class=topicref> <a data-id=DBMessageDetails href=../../sea/tasks/DBMessageDetails.html> Message Details </a> </span><li><span class=topicref> <a data-id=DBModifyUser href=../../sea/tasks/DBModifyUser.html> Modify User </a> </span><li><span 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class=wh_search_button><span> Search </span></button></div></form></div><div class=container><div class=row><nav class="wh_tools hidden-print"><div class=wh_breadcrumb><ol class=hidden-print><li><span class=home> <a href=../../index.html> <span> Home </span> </a> </span><li><span class=topicref> <a href=../../sea/concepts/Configuration.html> Configuration </a> </span><li><span class=topicref> <a href=../../sea/concepts/ConfigPolicy.html> Policy </a> </span><li><span class=topicref> <a href=../../sea/concepts/ConfigPolEncryption.html> Encryption </a> </span><li><span class=topicref> <a href=../../sea/concepts/ConfigPolEncryptTLS.html> Encryption: TLS </a> </span><li class=active><span class=topicref> Transport Layer Security (TLS) Email Encryption </span></ol></div><div class="wh_right_tools hidden-sm hidden-xs"><div class=wh_navigation_links><span class=navheader id=topic_navigation_links> </span></div><div class="wh_print_link print"><a title="Print this page"href=javascript:window.print();> </a></div></div></nav></div><div class=wh_content_area><div class=row><div class="col-lg-8 col-md-8 col-sm-8 col-xs-12"><div class="wh_topic_content body"><main role=main><article aria-labelledby=ariaid-title1 role=article><h1 class="title topictitle1"id=ariaid-title1>Transport Layer Security (TLS) Email Encryption</h1><div class="body refbody"><section class=section><h2 class="title sectiontitle">Transport Layer Security (TLS) in the Email Appliance</h2><p class=p>Transport Layer Security (TLS) enables the encrypted communication of messages between hosts that support TLS and can also allow one host to verify the identity of another. On the Email Appliance, TLS is set to <span class="ph uicontrol"> Off </span> by default. In this state, the Email Appliance will never attempt to encrypt email or verify the identity of a host to which it sends email.</section><section class=section><h2 class="title sectiontitle">Establishing a TLS connection</h2><p class=p>Once <span class="ph uicontrol"> Email Encryption (TLS) </span> is set to <span class="ph uicontrol"> On </span> , the Email Appliance will offer to encrypt incoming email by default. Other TLS-capable mail relays can then encrypt email sent to the Email Appliance. The appliance will also attempt to use TLS encryption for outbound email. To encrypt email, a TLS session must be established as follows:<div class=p><div class=tablenoborder><table border=1 cellpadding=4 cellspacing=0 class=table frame=void rules=rows><colgroup><col><col></colgroup><tbody class=tbody><tr><td class="entry nocellnorowborder"><img class=image src=../images/tls.gif><td class="entry nocellnorowborder"><p class=p>1. A connection is established between the Email Appliance and the other mail relay.</p> <p class=p>2. The receiving host offers TLS encryption.</p> <p class=p>3. The sending host starts a TLS session.</p> <p class=p>4. The Email Appliance and the other relay attempt to exchange encryption ciphers.</p></table></div></div><div class="note note"><div class=notetitle>Note</div> The host sending the mail is responsible for whether encryption is used. The receiving host can not require the sending host to encrypt email that it sends.</div></section><section class=section><h2 class="title sectiontitle">Encryption and Identity Verification</h2><p class=p>When email is encrypted, it cannot be read by anyone who does not have the appropriate key to decrypt it. However, encryption by itself does not allow you to verify the identity of the person or organization to whom you are sending the encrypted email. It is conceivable that the encrypted email could be redirected and read if the identity of the receiving mail relay has not been verified. To prevent this, the Email Appliance can be configured to use <a class=xref href=certificates.html> certificates </a> to verify the identity of the TLS-capable host receiving that is receiving email.</section><section class=section><h2 class="title sectiontitle">Setting Policies for Specific Domains</h2><p class=p>The Email Appliance can be configured to use specific policies for email that is sent to and from particular domains, including requiring the verification of the identity of a mail relay. Available policies include:<p class=p><strong class="ph b"> Incoming Domains </strong><ul class=ul><li class=li><span class="ph uicontrol"> Attempt Encryption: </span> When this option is selected and TLS is set to <span class="ph uicontrol"> On </span> , the Email Appliance will attempt, but not require, the use of TLS encryption for all incoming email. When an email relay attempts to send mail to the Email Appliance: <div class=tablenoborder><table border=1 cellpadding=4 cellspacing=0 class=table frame=void rules=rows><colgroup><col><col></colgroup><tbody class=tbody><tr><td class="entry nocellnorowborder"><img class=image src=../images/tls_attempt-in.gif><td class="entry nocellnorowborder"><p class=p></p> <p class=p>1. A TLS connection sequence and cipher exchange will be attempted (as shown above in <span class="ph uicontrol"> Establishing a TLS connection </span> ).</p> <p class=p>2a. If the sequence is successful, email sent by the mail relay to the Email Appliance will be encrypted.</p> <p class=p>2b. If the TLS session or cipher exchange fails, the Email Appliance will still receive mail from the other mail relay, but the mail will not be encrypted.</p></table></div><li class=li><span class="ph uicontrol"> Require Encryption: </span> Selecting this policy ensures that the mail relay will send email from the specified domain only if the Email Appliance supports TLS encryption. The mail relay will also check if the Email Appliance has a valid certificate. If the certificate check fails, the mail relay will still send encrypted email. <div class=tablenoborder><table border=1 cellpadding=4 cellspacing=0 class=table frame=void rules=rows><colgroup><col><col></colgroup><tbody class=tbody><tr><td class="entry nocellnorowborder"><img class=image src=../images/tls_require-in.gif><td class="entry nocellnorowborder"><p class=p></p> <p class=p>1. A TLS connection sequence and cipher exchange will be attempted (as shown above in <span class="ph uicontrol"> Establishing a TLS connection </span> ).</p> <p class=p>2a. If the sequence is successful, email sent by the mail relay to the Email Appliance will be encrypted.</p> <p class=p>2b. If the sequence fails, the mail relay will not send mail to the Email Appliance.</p></table></div><li class=li><span class="ph uicontrol"> Require Encryption and Validate Certificate: </span> Selecting this policy ensures that the mail relay will only send email if the Email Appliance supports TLS encryption, and also has a valid certificate that has been signed by a trusted certificate authority. This ensures that the email is encrypted and that the identity of the Email Appliance can be confirmed. <div class=tablenoborder><table border=1 cellpadding=4 cellspacing=0 class=table frame=void rules=rows><colgroup><col><col></colgroup><tbody class=tbody><tr><td class="entry nocellnorowborder"><img class=image src=../images/tls_verify-in.gif><td class="entry nocellnorowborder"><p class=p>1. A TLS connection sequence and cipher exchange will be attempted (as shown above in <span class="ph uicontrol"> Establishing a TLS connection </span> ).</p> <p class=p>2. The mail relay will retrieve the Email Appliance mail certificate and authenticate it.</p> <p class=p>3a. If the connection sequence is successful and the identity of the mail relay can be verified, email sent by the relay to the Email Appliance will be encrypted.</p> <p class=p>3b. If the connection sequence fails, or if the identity verification fails, the mail relay will not send mail to the Email Appliance.</p></table></div></ul><p class=p><strong class="ph b"> Outgoing Domains </strong><ul class=ul><li class=li><span class="ph uicontrol"> Attempt Encryption: </span> When this option is selected and TLS is set to <span class="ph uicontrol"> On </span> , the Email Appliance will attempt, but not require, the use of TLS encryption for all outgoing email. When the Email Appliance attempts to send mail to a mail relay: <div class=tablenoborder><table border=1 cellpadding=4 cellspacing=0 class=table frame=void rules=rows><colgroup><col><col></colgroup><tbody class=tbody><tr><td class="entry nocellnorowborder"><img class=image src=../images/tls_attempt-out.gif><td class="entry nocellnorowborder"><p class=p>1. A TLS connection sequence and cipher exchange will be attempted (as shown above in <span class="ph uicontrol"> Establishing a TLS connection </span> ).</p> <p class=p>2a. If the sequence is successful, email sent by the Email Appliance to the other host will be encrypted.</p> <p class=p>2b. If the TLS session or cipher exchange fails, or the other host does not support TLS, the Email Appliance will still send email to the other host, but the email will not be encrypted.</p></table></div><li class=li><span class="ph uicontrol"> Prevent Encryption: </span> No attempt is made to encrypt email, even if encryption is supported by the receiving host. This may be useful in cases where encryption is not necessary, and attempts to use TLS encryption are having a performance impact. <div class=tablenoborder><table border=1 cellpadding=4 cellspacing=0 class=table frame=void rules=rows><colgroup><col><col></colgroup><tbody class=tbody><tr><td class="entry nocellnorowborder"><img class=image src=../images/tls_prevent-out.gif><td class="entry nocellnorowborder"><p class=p></p> <p class=p>1. The Email Appliance will connect to the other mail relay.</p> <p class=p>2. Email sent by the Email Appliance to the other mail relay will not be encrypted.</p></table></div><li class=li><span class="ph uicontrol"> Require Encryption: </span> Selecting this policy ensures that the Email Appliance will send email to the specified domain only if the receiving host supports TLS encryption. The Email Appliance will also check if the host has a valid certificate. If the certificate check fails, the Email Appliance will still send encrypted email. However, it will not be possible to confirm the identity of the receiving host. <div class=tablenoborder><table border=1 cellpadding=4 cellspacing=0 class=table frame=void rules=rows><colgroup><col><col></colgroup><tbody class=tbody><tr><td class="entry nocellnorowborder"><img class=image src=../images/tls_require-out.gif><td class="entry nocellnorowborder"><p class=p></p> <p class=p>1. A TLS connection sequence and cipher exchange will be attempted (as shown above in <span class="ph uicontrol"> Establishing a TLS connection </span> ).</p> <p class=p>2a. If the sequence is successful, email sent by the Email Appliance to the other mail relay will be encrypted.</p> <p class=p>2b. If the sequence fails, the Email Appliance will not send email to the other mail relay.</p></table></div><li class=li><span class="ph uicontrol"> Require Encryption and Validate Certificate: </span> Selecting this policy ensures that the Email Appliance will only send email if the receiving host supports TLS encryption, and also has a valid certificate that has been signed by a trusted certificate authority. This ensures that the email has both been encrypted and that the identity of the receiving host has been confirmed. <div class=tablenoborder><table border=1 cellpadding=4 cellspacing=0 class=table frame=void rules=rows><colgroup><col><col></colgroup><tbody class=tbody><tr><td class="entry nocellnorowborder"><img class=image src=../images/tls_verify-out.gif><td class="entry nocellnorowborder"><p class=p>1. A TLS connection sequence and cipher exchange will be attempted (as shown above in <span class="ph uicontrol"> Establishing a TLS connection </span> ).</p> <p class=p>2. The Email Appliance will retrieve the mail relayâs certificate and authenticate it.</p> <p class=p>3a. If the connection sequence is successful and the identity of the mail relay can be verified, email sent by the Email Appliance to the other mail relay will be encrypted.</p> <p class=p>3b. If the connection sequence fails, or if the identity verification fails, the Email Appliance will not send email to the other mail relay.</p></table></div></ul><div class="note note"><div class=notetitle>Note</div> After the Email Appliance has passed encrypted email to another mail relay, there is no way to guarantee it will remain encrypted or confidential, even if the identity of the other relay has been verified. You may need to communicate with the organization that manages the other relay if this is a concern.</div></section></div></article></main></div><div class=wh_related_links><nav class=related-links role=navigation><div class="linklist linklist relinfo relconcepts"><strong> Related concepts </strong><br><div class=related_link><a class=navheader_parent_path href=../concepts/ConfigPolEncryption.html title=Encryption> Encryption </a></div><div class=related_link><a class=navheader_parent_path href=../concepts/ConfigSysCertificates.html title=Certificates> Certificates </a></div></div><div class="linklist linklist relinfo relref"><strong> Related reference </strong><br><div class=related_link><a title="Certificates and Certificate Authorities"class=navheader_parent_path href=certificates.html> Certificates and Certificate Authorities </a></div><div class=related_link><a title="Obtaining a Certificate for the Email Appliance"class=navheader_parent_path href=csr_request.html> Obtaining a Certificate for the Email Appliance </a></div></div><div class="linklist linklist relinfo reltasks"><strong> Related tasks </strong><br><div class=related_link><a title="Activating Email Encryption"class=navheader_parent_path href=../tasks/ConfigPolEncryptOn.html> Activating Email Encryption </a></div><div class=related_link><a title="Advanced Encryption Policy"class=navheader_parent_path href=../tasks/ConfigPolEncryptDomains.html> Advanced Encryption Policy </a></div><div class=related_link><a title="Deleting a Domain"class=navheader_parent_path href=../tasks/ConfigPolEncryptDelete.html> Deleting a Domain </a></div></div></nav></div></div><nav class="col-lg-4 col-md-4 col-sm-4 col-xs-12 navbar"id=wh_side_toc role=navigation><div class=wh_side_toc><ul class=hidden-print><li><span class=topicref> <a href=../../sea/concepts/Configuration.html> Configuration </a> </span> <ul class="nav nav-list"><li><span class=topicref> <a href=../../sea/concepts/ConfigAccounts.html> Accounts </a> </span><li><span class=topicref> <a href=../../sea/concepts/ConfigPolicy.html> Policy </a> </span> <ul class="nav nav-list"><li><span class=topicref> <a href=../../sea/references/policy_flow.html> Policy Message Flow </a> </span><li><span class=topicref> <a href=../../sea/references/ConfigPolAntiVirusRef.html> Threat Protection </a> </span><li><span class=topicref> <a href=../../sea/references/ConfigPolAntiSpamRef.html> Anti-Spam </a> </span><li><span class=topicref> <a href=../../sea/references/DataControlRef.html> Data Control </a> </span><li><span class=topicref> <a href=../../sea/references/ConfigPolContentRef.html> Additional Policy </a> </span><li><span class=topicref> <a href=../../sea/tasks/ConfigPolAllowBlockLists.html> Allow/Block Lists </a> </span><li><span class=topicref> <a href=../../sea/concepts/ConfigPolFilteringOptions.html> Filtering Options </a> </span><li><span class=topicref> <a href=../../sea/concepts/ConfigPolSandstorm.html> Sandstorm </a> </span><li><span class=topicref> <a href=../../sea/concepts/ConfigPolEncryption.html> Encryption </a> </span> <ul class="nav nav-list"><li><span class=topicref> <a href=../../sea/concepts/ConfigPolEncryptTLS.html> Encryption: TLS </a> </span> <ul class="nav nav-list"><li><span class=topicref> <a href=../../sea/tasks/ConfigPolEncryptOn.html> Activating Email Encryption </a> </span><li><span class=topicref> <a href=../../sea/tasks/ConfigPolEncryptDomains.html> Advanced Encryption Policy </a> </span><li><span class=topicref> <a href=../../sea/tasks/ConfigPolEncryptDelete.html> Deleting a Domain </a> </span><li class=active><span class=topicref> Transport Layer Security (TLS) Email Encryption </span></ul><li><span class=topicref> <a href=../../sea/concepts/ConfigPolEncryptSPXMain.html> Encryption: SPX </a> </span></ul><li><span class=topicref> <a href=../../sea/tasks/ConfigPolSMTP_Auth.html> SMTP Authentication </a> </span><li><span class=topicref> <a href=../../sea/concepts/ConfigPolSMTP_Opts.html> SMTP Options </a> </span></ul><li><span class=topicref> <a href=../../sea/concepts/ConfigSystem.html> System </a> </span><li><span class=topicref> <a href=../../sea/concepts/ConfigMailRouting.html> Routing </a> </span><li><span class=topicref> <a href=../../sea/concepts/ConfigNetwork.html> Network </a> </span></ul></ul></div></nav></div></div></div><nav class="navbar navbar-default wh_footer"><div class="footer-container text-center"><a href=http://www.sophos.com shape=rect> <div style="display: inline-block !important;"class=sophos_footer_logo></div> <div style="display: inline !important;"class=sophos_footer_copyright>Â© 2018 Sophos Limited. 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