Although radio frequency is a rate of oscillation, the term radio frequency or its abbreviation RF are used as a synonym for radio â i.e., to describe the use of wireless communication, as opposed to communication via electric wires.Examples include:1  Radio-frequency identification.owever, since the antenna will pick up thousands of radio signals at a time, a radio tuner is necessary to tune into a particular frequency (or frequency range). This is typically done via a resonator â in its simplest form, a circuit with a capacitor and an inductor form a tuned circuit.
Simple Mail Transfer Protocol (SMTP) is an Internet standard for electronic mail (email) transmission. First defined by RFC 821 in 1982, it was last updated in 2008 with the Extended SMTP additions by RFC 5321 âwhich is the protocol in widespread use today. SMTP by default uses TCP port 25.The protocol for mail submission is the same, but uses port 587.SMTP connections secured by SSL, known as SMTPS, default to port 465 (nonstandard, but sometimes used for legacy reasons).mail is submitted by a mail client (MUA, mail user agent) to a mail server (MSA, mail submission agent) using SMTP on TCP port 587. Most mailbox providers still allow submission on traditional port 25. From there, the MSA delivers the mail to its mail transfer agent (MTA, mail transfer agent).
When POP3 clients send messages, the Exchange Server computer is communicating with an SMTP (Simple Mail Transfer Protocol) host. This requires access to TCP port 25. The Internet Mail Connector and the Internet Mail Service use TCP port 25 for inbound SMTP messages as defined by RFC-821.or the LDAP client to connect to the Exchange Server computer, the ports that need to be configured on the firewall are based purely on the authentication method in use. With Basic authentication, the Exchange Server computer listens on port 389.