<sod>Using a [[mail submission agent]] (MSA), generally on port 587, implies SMTP AUTH. MSA usage is supported by most software<ref>{{cite web |url=http://www.ietf.org/iesg/implementation/report-rfc2476.txt |title=Message Submission Interoperability Report |author=Randall Gellens |date=January 19, 2005 |publisher=[[IETF]] |accessdate=2010-05-30}}</ref> and is recommended, especially to support nomadic users, as several network hubs either block port 25 or use [[SMTP proxy|SMTP proxies]]. The MSA is responsible for ensuring that the message envelope contains good addresses, and may enforce local policies for the ''<code>From</code>'' header field. Verifying that the envelope sender (a.k.a. ''<code>Return-Path</code>'') used for [[Sender Policy Framework|SPF]] and the ''From'' address agree with the authenticated ''user-id'' is particularly important for domains that sign messages using [[DomainKeys Identified Mail|DKIM]].<eod>
<sod>Using a [[mail submission agent]] (MSA), generally on port 587, implies SMTP AUTH. MSA usage is supported by most software<ref>{{cite web |url=http://www.ietf.org/iesg/implementation/report-rfc2476.txt |title=Message Submission Interoperability Report |author=Randall Gellens |date=January 19, 2005 |publisher=[[IETF]] |accessdate=2010-05-30}}</ref> and is recommended, especially to support nomadic users, as several network hubs either block port 25 or use [[SMTP proxy|SMTP proxies]]. The MSA is responsible for ensuring that the message envelope contains good addresses, and may enforce local policies for the ''<code>From</code>'' header field. Verifying that the [[envelope sender]] (a.k.a. ''<code>Return-Path</code>'') used for [[Sender Policy Framework|SPF]] and the ''From'' address agree with the authenticated ''user-id'' is particularly important for domains that sign messages using [[DomainKeys Identified Mail|DKIM]].<eod>