New Dovecot service: SMTP Submission (RFC6409)

[Tanstaafl]

This is fantastic Stephan! Especially since I'll soon be rolling a new
Dovecot server to act as a backup for our current Office 365 mail, as
well as to be prepared in case I can ever talk the boss into migrating
back to dovecot (we were using Dovecot for a really long time until he
was convinced by others that we 'had' to be on Office 365).

I'll also be setting up a shiny new VPS for my own private mail server,
to provide better service that I currently get from my shared Dreamhost
account.

But can you confirm...

Would this also be called 'BURL' support?

And will this initial implementation work with current Postfix to
provide the basic Save-To-Sent feature?

I seem to recall there was some minor code required on the Postfix side,
and Wietse seemed to not have a problem implementing it, but had asked
about any IMAP Clients supporting BURL...

If this won't work with current versions of Postfix, maybe you or Timo
or someone could go poke him now that Dovecot supports it?

Anyway, thanks again, I'm really looking forward to being able to do
away with the 'Save-To-Sent' wastage.


On 12/11/2017, 6:14:26 PM, Stephan Bosch <stephan at rename-it.nl> wrote:
> Hi,
> 
> As some of you know, I started implementing the SMTP submission proxy a
> few years ago. It acts as a front-end for any MTA, adding the necessary
> functionality for an SMTP submission service, also known as a Mail
> Submission Agent (MSA) (https://tools.ietf.org/html/rfc6409). The main
> reason I created this, back then, was implementing the BURL capability
> (https://tools.ietf.org/html/rfc4468). The main application of that
> capability -- together with IMAP URLAUTH -- 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. Apart from BURL, the submission proxy service 
> also adds the required AUTH support, avoiding the need to configure the
> MTA for SASL authentication. More SMTP capabilities like CHUNKING and
> SIZE are supported, without requiring the backend MTA supporting these
> extensions. Other capabilities like DSN currently require support from
> the backend/relay MTA.
> 
> At this point, 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 we could do are adding Sieve 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.
> 
> The reason I send this message now, is that this code is finally merged
> into the Dovecot master repository. This means that it is part of the
> upcoming 2.3 release. Now that it is merged, you can install and test it
> from Github if you like. Feedback is of course appreciated. The
> documentation is still pretty sparse, but there is currently not much to
> configure. Just add "submission" to the protocols and configure the
> relay MTA server. The configuration is currently only documented in the
> example configuration in doc/example-config/conf.d/20-submission.conf.
> The submission service is a login service, just like IMAP, POP3 and
> ManageSieve, so clients are required to authenticate. The same
> authentication configuration 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.
> 
> I've updated the automated Xi Debian package builder to create an
> additional dovecot-submissiond package. So, if you're using the Xi
> packages, you only need to install that package and configure the relay MTA.