Editing Email client (section)

==Protocols==
Popular protocols for retrieving mail include [[POP3]] and [[IMAP4]]. Sending mail is usually done using the [[SMTP]] protocol.

Another important standard supported by most email clients is [[MIME]], which is used to send [[binary file]] [[email attachment]]s. Attachments are files that are not part of the email proper but are sent with the email.

Most email clients use a ''User-Agent''<ref>{{cite IETF |title=Netnews Article Format |rfc=5536 |sectionname=User-Agent |section=3.2.13 |date=November 2009 |publisher=[[Internet Engineering Task Force|IETF]] |quote=Some of this information has previously been sent in non-standardized header fields such as X-Newsreader, X-Mailer, X-Posting-Agent, X-Http-User-Agent, and others}}</ref> [[header (computing)|header field]] to identify the software used to send the message. This header field is defined for Netnews, but not-for e-mail, and, as such, is non-standard<ref>{{cite IETF
 | title       = Common Internet Message Headers
 | rfc         = 2076
 | date        = February 1997
 | author      = J. Palme
 | section     = 2
 | sectionname = Use of gatewaying headers
 | quote       = Headers defined only in RFC 1036 for use in Usenet News sometimes appear in mail messages, either because the messages have been gatewayed from Usenet News to e-mail, or because the messages were written in combined clients supporting both e-mail and Usenet News in the same client. These headers are not standardized for use in Internet e-mail and should be handled with caution by e-mail agents.
 | access-date = May 11, 2015
 }}
</ref> in e-mail headers.

{{IETF RFC|6409}}, ''Message Submission for Mail'', details the role of the [[Mail submission agent]].

{{IETF RFC|5068}}, ''Email Submission Operations: Access and Accountability Requirements'', provides a survey of the concepts of MTA, MSA, MDA, and MUA. It mentions that "'' Access Providers MUST NOT block users from accessing the external Internet using the SUBMISSION port 587''" and that "''MUAs SHOULD use the SUBMISSION port for message submission.''"

{{IETF RFC|5965}}, ''An Extensible Format for Email Feedback Reports'', provides "an extensible format and MIME type that may be used by mail operators to report feedback about received email to other parties." 

===Port numbers===
Email servers and clients by convention use the [[List of TCP and UDP port numbers|TCP port numbers]] in the following table.  For MSA, IMAP and POP3, the table reports also the labels that a client can use to query the [[SRV record]]s and discover both the host name and the port number of the corresponding service.<ref>{{cite IETF |title=Use of SRV Records for Locating Email Submission/Access Services |rfc=6186 |author=Cyrus Daboo |date=March 2011 |publisher=[[Internet Engineering Task Force|IETF]] |access-date=17 April 2013}}</ref>
{| class="wikitable"
|-
! Protocol
! Use
! Plain text or <br>encrypt sessions
! Plain text <br>sessions only
! Encrypt sessions <br>only
|-
| [[Post Office Protocol|POP3]]
| incoming mail
| style="text-align: right;" | 110 <br>_pop3._tcp
|
| style="text-align: right;" | 995 <br>_pop3s._tcp
|-
| [[Internet Message Access Protocol|IMAP4]]
| incoming mail
| style="text-align: right;" | 143 <br>_imap._tcp
|
| style="text-align: right;" | 993 <br>_imaps._tcp
|-
| [[Simple Mail Transfer Protocol|SMTP]]
| outgoing mail
| style="text-align: right;" | 25
|
|style="text-align: right;" |587
|-
| [[Mail submission agent|MSA]]
| outgoing mail
| style="text-align: right;" | 587 <br>_submission._tcp
|
| style="text-align: right;" | 465<ref>{{cite IETF |title=Cleartext Considered Obsolete: Use of Transport Layer Security (TLS) for Email Submission and Access |rfc=8314 |author1=Keith Moore |author2=Chris Newman |date=January 2018 |publisher=[[Internet Engineering Task Force|IETF]] |access-date=12 February 2018}}</ref> <br>_submissions._tcp
|-
| [[HTTP]]
| webmail
|
| style="text-align: right;" | 80
| style="text-align: right;" | 443
|}

While webmail obeys the earlier HTTP disposition of having separate ports for encrypt and plain text sessions, mail protocols use the [[STARTTLS]] technique, thereby allowing encryption to start on an already established TCP connection. While {{IETF RFC|2595}} used to discourage the use of the previously established ports 995 and 993, {{IETF RFC|8314}} promotes the use of implicit [[Transport Layer Security|TLS]] when available.

===Proprietary client protocols===
[[Microsoft]] mail systems use the [[proprietary software|proprietary]] [[Messaging Application Programming Interface]] (MAPI) in client applications, such as [[Microsoft Outlook]], to access [[Microsoft Exchange Server|Microsoft Exchange]] electronic mail servers.