Operation Manual

Either an end-user's email client, a.k.a. MUA (Mail User Agent), or a relaying server's MTA (Mail
Transport Agents) can act as an SMTP client. An email client knows the outgoing mail SMTP server
from its configuration. A relaying server typically determines which SMTP server to connect to by
looking up the MX (Mail eXchange) DNS record for each recipient's domain name (the part of the
email address to the right of the at (@) sign). Conformant MTAs (not all) fall back to a simple A
record in the case of no MX. Some current mail transfer agents will also use SRV records, a more
general form of MX, though these are not widely adopted. (Relaying servers can also be configured
to use a smart host.) The SMTP client initiates a TCP connection to server's port 25 (unless
overridden by configuration). SMTP is a "push" protocol that does not allow one to "pull" messages
from a remote server on demand.
Tip: If you are not sure whether to use POP3 or IMAP protocol, then use IMAP
because of significant advantages over POP3.
Copyright © 2016 eM Client, Inc.
440 N. Wolfe Road
Sunnyvale, CA 94085
California, USA
[e-mail]