Editing Message transfer agent (section)

==Transfer versus access==
A relay or filtering server will typically store email only briefly, but other systems keep full [[Email box|mailboxes]] for email - in which case they usually support some means for end users to access their email via a Mail User Agent (MUA), or [[email client]].

Common protocols for this are:
* [[Post Office Protocol]] (POP3)
* [[Internet Message Access Protocol]] (IMAP)
* Proprietary systems, such as Microsoft's [[MAPI]]

Submission of new email from a mail client is via SMTP, typically on port 587 or 465, and is now generally restricted to servers the user has an account with-such as their [[ISP]]. This is for policy, not technical, reasons so that providers have some means of holding their users accountable for the generation of [[Spam (electronic)|spam]] and other forms of email abuse.<ref>{{cite web |author=Bill Cole |title=What are the IPs that sends mail for a domain? |url=http://www.ietf.org/mail-archive/web/asrg/current/msg15593.html |date=29 June 2009 |work=[[Anti-Spam Research Group|ASRG]] mailing list |access-date=15 September 2009}}</ref>