title: Swiftmailer: Unable to connect with TLS encryption
body: <p>I'm trying to send emails via Symfony with Swiftmailer. On the production server I get an error:</p>
  
  <pre><code>[2016-08-20 11:59:37] app.ERROR: Exception occurred while flushing email queue: Unable to connect with TLS encryption [] []
  </code></pre>
  
  <p>This is what I have in my config.yml:</p>
  
  <pre><code>swiftmailer:
  transport: smtp
  host:      localhost
  username:  info@derkvanderheide.nl
  password:  testpw
  spool:     { type: memory }
  encryption: tls
  port:       587
  </code></pre>
  
  <p>Postfix is my mailserver, it was installed with Plesk.</p>
  
  <p>This is my postfix main.cf:</p>
  
  <pre><code># See /usr/share/postfix/main.cf.dist for a commented, more complete version
  
  
  # Debian specific:  Specifying a file name will cause the first
  # line of that file to be used as the name.  The Debian default
  # is /etc/mailname.
  #myorigin = /etc/mailname
  
  smtpd_banner = $myhostname ESMTP $mail_name (Ubuntu)
  biff = no
  
  # appending .domain is the MUA's job.
  append_dot_mydomain = no
  
  # Uncomment the next line to generate "delayed mail" warnings
  #delay_warning_time = 4h
  
  readme_directory = no
  
  # TLS parameters
  smtpd_tls_cert_file = /etc/ssl/certs/smtpd.crt
  smtpd_tls_key_file = /etc/ssl/private/smtpd.key
  smtpd_use_tls = yes
  smtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scache
  smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache
  
  # See /usr/share/doc/postfix/TLS_README.gz in the postfix-doc package for
  # information on enabling SSL in the smtp client.
  
  smtpd_relay_restrictions = permit_mynetworks permit_sasl_authenticated defer_unauth_destination
  myhostname = derkvanderheide.nl
  alias_maps = hash:/etc/aliases, hash:/var/spool/postfix/plesk/aliases
  alias_database = hash:/etc/aliases
  mydestination = localdomain, localhost, localhost.localdomain, localhost
  relayhost =
  mynetworks =
  mailbox_command = procmail -a "$EXTENSION"
  mailbox_size_limit = 0
  recipient_delimiter = +
  inet_interfaces = all
  inet_protocols = all
  virtual_mailbox_domains = $virtual_mailbox_maps, hash:/var/spool/postfix/plesk/virtual_domains
  virtual_alias_maps = $virtual_maps, hash:/var/spool/postfix/plesk/virtual
  virtual_mailbox_maps = , hash:/var/spool/postfix/plesk/vmailbox
  transport_maps = , hash:/var/spool/postfix/plesk/transport
  smtpd_tls_security_level = encrypt
  smtp_tls_security_level = may
  smtp_use_tls = yes
  smtpd_timeout = 3600s
  smtpd_proxy_timeout = 3600s
  disable_vrfy_command = yes
  smtpd_sender_restrictions = check_sender_access hash:/var/spool/postfix/plesk/blacklists, permit_sasl_authenticated
  smtpd_client_restrictions = permit_mynetworks, permit_sasl_authenticated
  smtp_send_xforward_command = yes
  smtpd_authorized_xforward_hosts = 127.0.0.0/8 [::1]/128
  smtpd_sasl_auth_enable = yes
  smtpd_recipient_restrictions = permit_mynetworks, permit_sasl_authenticated, reject_unauth_destination
  virtual_mailbox_base = /var/qmail/mailnames
  virtual_uid_maps = static:30
  virtual_gid_maps = static:31
  smtpd_milters = , inet:127.0.0.1:12768
  sender_dependent_default_transport_maps = hash:/var/spool/postfix/plesk/sdd_transport_maps
  virtual_transport = plesk_virtual
  plesk_virtual_destination_recipient_limit = 1
  mailman_destination_recipient_limit = 1
  virtual_mailbox_limit = 0
  smtpd_tls_mandatory_protocols = TLSv1 TLSv1.1 TLSv1.2
  smtpd_tls_protocols = TLSv1 TLSv1.1 TLSv1.2
  smtpd_tls_ciphers = medium
  smtpd_tls_mandatory_ciphers = medium
  tls_medium_cipherlist = HIGH:!aNULL:!MD5
  message_size_limit = 10240000
  smtpd_tls_auth_only = no
  smtp_tls_note_starttls_offer = yes
  smtpd_tls_CAfile = /etc/ssl/certs/cacert.pem
  smtpd_tls_loglevel = 1
  smtpd_tls_received_header = yes
  smtpd_tls_session_cache_timeout = 3600s
  tls_random_source = dev:/dev/urandom
  </code></pre>
  
  <p>This is the output from telnet: </p>
  
  <pre><code>Trying 185.57.10.237...
  Connected to derkvanderheide.nl.
  Escape character is '^]'.
  220 derkvanderheide.nl ESMTP Postfix (Ubuntu)
  ehlo localhost
  250-derkvanderheide.nl
  250-PIPELINING
  250-SIZE 10240000
  250-ETRN
  250-STARTTLS
  250-ENHANCEDSTATUSCODES
  250-8BITMIME
  250 DSN
  </code></pre>
  
  <p>This is in my maillog:</p>
  
  <pre><code>Aug 20 17:06:35 vps-248826-4222 postfix/smtpd[8592]: connect from vps-248826-4222.hosted.at.hostnet.nl[127.0.0.1]
  Aug 20 17:06:35 vps-248826-4222 postfix/smtpd[8592]: SSL_accept error from vps-248826-4222.hosted.at.hostnet.nl[127.0.0.1]: 0
  Aug 20 17:06:35 vps-248826-4222 postfix/smtpd[8592]: warning: TLS library problem: error:14094418:SSL routines:SSL3_READ_BYTES:tlsv1 alert unknown ca:s3_pkt.c:1262:SSL alert number 48:
  Aug 20 17:06:35 vps-248826-4222 postfix/smtpd[8592]: lost connection after STARTTLS from vps-248826-4222.hosted.at.hostnet.nl[127.0.0.1]
  Aug 20 17:06:35 vps-248826-4222 postfix/smtpd[8592]: disconnect from vps-248826-4222.hosted.at.hostnet.nl[127.0.0.1]
  </code></pre>
  
  <p>I have barely any clue what I'm doing, this is my first time messing around with a mail server.</p>