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diff --git a/doc/wiki/Submission.txt b/doc/wiki/Submission.txt new file mode 100644 index 0000000..46bafb3 --- /dev/null +++ b/doc/wiki/Submission.txt @@ -0,0 +1,191 @@ +Submission Server +================= + +As of version 2.3.0, Dovecot provides an SMTP submission service, also known as +a Mail Submission Agent (MSA) [https://tools.ietf.org/html/rfc6409]. It is +currently implemented as a proxy that acts as a front-end for any <MTA.txt>, +adding the necessary functionality required for a submission service: it adds +the required AUTH [https://tools.ietf.org/html/rfc4954] support, avoiding the +need to configure the MTA for SASL authentication. More SMTP capabilities like +CHUNKING [https://tools.ietf.org/html/rfc3030] and SIZE +[https://tools.ietf.org/html/rfc1870] are supported, without requiring the +backend MTA supporting these extensions. Other capabilities like 8BITMIME +[https://tools.ietf.org/html/rfc6152] and DSN +[https://tools.ietf.org/html/rfc3461] currently require support from the +backend/relay MTA. + +The most notable feature that the proxy adds is the BURL capability +[https://tools.ietf.org/html/rfc4468]. The main application of that +capabilitytogether with <IMAP> [IMAPServer.txt] URLAUTH +[https://tools.ietf.org/html/rfc4467]is avoiding a duplicate upload of +submitted e-mail messages; normally the message is both sent through SMTP and +uploaded to the "Sent" folder through IMAP. Using BURL, the client can first +upload the message to IMAP and then use BURL to make the SMTP server fetch the +message from IMAP for submission, thereby avoiding a second upload. Few clients +currently support the BURL capability, but once it becomes available on the +server side, client developers will at least have some incentive to provide +support for this feature. + +*NOTE:* Currently, the submission proxy is still pretty basic. However, it will +provide a basis for adding all kinds of functionality in the (not so distant) +future. For the first time, it will be possible to act upon message submission, +rather than only message retrieval; e.g. plugins can be devised that process +outgoing messages somehow. Examples of the things that could be implemented are +adding <Sieve> [Pigeonhole.txt] filtering support for outgoing messages, or +implicitly storing submitted messages to the Sent folder. Once a plugin API is +devised, you can create your own plugins. + +Features +-------- + +The following SMTP capabilities are supported by the Dovecot submission +service: + + * 8BITMIME [https://tools.ietf.org/html/rfc6152] - Only if relay MTA provides + support + * AUTH [https://tools.ietf.org/html/rfc4954] + * BURL [https://tools.ietf.org/html/rfc4468] + * CHUNKING [https://tools.ietf.org/html/rfc3030] + * DSN [https://tools.ietf.org/html/rfc3461] - Only if relay MTA provides + support + * ENHANCEDSTATUSCODES [https://tools.ietf.org/html/rfc2034] + * PIPELINING [https://tools.ietf.org/html/rfc2920] + * SIZE [https://tools.ietf.org/html/rfc1870] + * STARTTLS [https://tools.ietf.org/html/rfc3207] + * VRFY [https://tools.ietf.org/html/rfc5321] + * XCLIENT [http://www.postfix.org/XCLIENT_README.html] + +Configuration +------------- + +Submission Service +------------------ + +Just add 'submission' to the 'protocols=' setting and configure the relay MTA +server. The submission service is a login service, just like IMAP, POP3 and +<ManageSieve> [Pigeonhole.ManageSieve.txt], so clients are required to +authenticate. The same <authentication configuration> [Authentication.txt] will +also apply to submission, unless you're doing protocol-specific things, in +which case you may need to amend your configuration for the new protocol. BURL +support requires a working IMAP URLAUTH implementation. + +The following settings apply to the Submission service: + +submission_logout_format = in=%i out=%o: + The SMTP Submission logout format string. The following variable + substitutions are supported: + %i : + Total number of bytes read from client + + %o : + Total number of bytes sent to client + + %{command_count} : + Number of commands received from client + + %{reply_count} : + Number of replies sent to client + + %{session} : + Session ID of the login session + + %{transaction_id} : + ID of the current transaction, if any + +hostname : + The host name reported by the SMTP service (and other parts of Dovecot), for + example to the client in the initial greeting and to the relay server in the + HELO/EHLO command. Default is the system's real hostname@domain. + +submission_max_mail_size : + The maximum size of messages accepted for relay. This announced in the SMTP + SIZE capability. If not configured, this is either determined from the relay + server or left unlimited if no limit is known (the relay MTA will reply with + error if some unknown limit exists there, which is duly passed to Dovecot's + client). + +submission_max_recipients : + Maximum number of recipients accepted per connection (default: unlimited). + +Relay MTA +--------- + +The Dovecot SMTP submission service directly proxies the mail transaction to +the SMTP relay configured with the following settings: + +submission_relay_host : + Host name for the relay server (required). + +submission_relay_port = 25 : + Port for the relay server. + +submission_relay_trusted = no : + Is the relay server trusted? This determines whether we try to send + (Postfix-specific) XCLIENT data to the relay server. + +submission_relay_user = : + User name for authentication to the relay MTA if authentication is required + there (authorization ID). + +submission_relay_master_user = : + Master user name for authentication to the relay MTA if authentication is + required there (authentication ID). + +submission_relay_password = : + Password for authentication to the relay MTA if authentication is required + there. + +submission_relay_ssl = no : + Indicates whether TLS is used for the connection to the relay server. The + following values are defined for this setting: + no : + No SSL is used. + + smtps : + An SMTPS connection (immediate SSL) is used. + + starttls : + The STARTTLS command is used to establish the TLS layer. + +submission_relay_ssl_verify = yes : + Configures whether the TLS certificate of the relay server is to be verified. + +submission_relay_rawlog_dir : + Write protocol logs for relay connection to this directory for debugging. + +See <Debugging.Rawlog.txt> for more details on rawlogs. + +Login Proxy +----------- + +Like IMAP and POP3, the Submission login service supports proxying to multiple +backend Dovecot servers. The <proxy configuration wiki page> +[PasswordDatabase.ExtraFields.Proxy.txt] for POP3 and IMAP applies +automatically to Submission as well. + +*IMPORTANT*: Please note that the login proxy described here is configured +between two Dovecot servers (e.g. director frontend and mail storage backend). +This is not the way to configure the relay connection between the Dovecot +submission service and the MTA! That is configured using the relay settings +described in the <previous section> [Submission.txt]. If you get this wrong, +things will seem to work (at least to some extent), but the service provided by +Dovecot will be effectively bypassed. + +Client Support +-------------- + +As of April 2019 there aren't many clients that support the BURL extension. ++-------------+-----------+-------------------------------------------------------------------------------------------------------+ +| *Client* | *Supports | *Notes* | +| | BURL?* | | ++-------------+-----------+-------------------------------------------------------------------------------------------------------+ +| Trojita | Yes | Mentioned on the dovecot discussion list | +| | | [http://dovecot.2317879.n4.nabble.com/New-Dovecot-service-SMTP-Submission-RFC6409-tp62117p62122.html] | ++-------------+-----------+-------------------------------------------------------------------------------------------------------+ +| Thunderbird | No | Vote on bugzilla [https://bugzilla.mozilla.org/page.cgi?id=voting/user.html&bug_id=421779] | ++-------------+-----------+-------------------------------------------------------------------------------------------------------+ +| KDE Akonadi | No | KDE bugzilla [https://bugs.kde.org/show_bug.cgi?id=408732] | +| / KMail | | | ++-------------+-----------+-------------------------------------------------------------------------------------------------------+ + +(This file was created from the wiki on 2019-06-19 12:42) |