Editing Simple Mail Transfer Protocol (section)

===Ports===
Communication between mail servers generally uses the standard [[Transmission Control Protocol|TCP]] port 25 designated for SMTP.

Mail ''clients'' however generally don't use this, instead using specific "submission" ports. Mail services generally accept email submission from clients on one of:

* 465 This port was deprecated after {{IETF RFC|2487}}, until the issue of {{IETF RFC|8314}}.
* 587 (Submission), as formalized in {{IETF RFC|6409}} (previously {{IETF RFC|2476}})

Port 2525 and others may be used by some individual providers, but have never been officially supported.

Many [[Internet service provider]]s now block all outgoing port 25 traffic from their customers. Mainly as an anti-spam measure,<ref>{{cite magazine |url=http://www.pcworld.com/article/116843/article.html |title=ISPs Pitch In to Stop Spam |author=Cara Garretson |year=2005 |magazine=[[PC World]] |access-date=18 January 2016 |quote=Last month, the Anti-Spam Technical Alliance, formed last year by Yahoo, America Online, EarthLink, and Microsoft, issued a list of antispam recommendations that includes filtering Port 25. |archive-date=August 28, 2015 |archive-url=https://web.archive.org/web/20150828005734/http://www.pcworld.com/article/116843/article.html |url-status=live }}</ref> but also to cure for the higher cost they have when leaving it open, perhaps by charging more from the few customers that require it open.

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