finish design docs (team#30608)

## Pager playbook

TODO: pager playbook

<!-- information about common errors from the monitoring system and -->

<!-- how to deal with them. this should be easy to follow: think of -->

<!-- your future self, in a stressful situation, tired and hungry. -->

No pager playbook has been built yet. See the [Monitoring and

testing](#monitoring-and-testing) section below for ideas on how to debug things.

## Disaster recovery

## SLA

TODO: <!-- describe an acceptable level of service for this service -->

There is no SLA specific to this service, but mail delivery is

generally considered to be high priority. Complaints about delivery

failure should be filed as [issues in our ticket tracker](#issues) and

addressed.

## Design

TODO: <!-- how this is built -->

<!-- should reuse and expand on the "proposed solution", it's a -->

<!-- "as-built" documented, whereas the "Proposed solution" is an -->

<!-- "architectural" document, which the final result might differ -->

<!-- from, sometimes significantly -->

The submission email service allows users to submit mail as if they

were on a `torproject.org` machine. Concretely, it is a Postfix server

which relays email to anywhere once [SASL authentication](https://en.wikipedia.org/wiki/Simple_Authentication_and_Security_Layer) is

passed.

<!-- a good guide to "audit" an existing project's design: -->

<!-- https://bluesock.org/~willkg/blog/dev/auditing_projects.html -->

Most of the code is glue code in Puppet, along with a small set of

patches to ud-ldap which were sent (and mostly accepted) upstream.

<!-- things to evaluate here:

### Authentication

 * services

 * storage (databases? plain text files? cloud/S3 storage?)

 * queues (e.g. email queues, job queues, schedulers)

 * interfaces (e.g. webserver, commandline)

 * authentication (e.g. SSH, LDAP?)

 * programming languages, frameworks, versions

 * dependent services (e.g. authenticates against LDAP, or requires

   git pushes)

 * deployments: how is code for this deployed (see also Installation)

SASL authentication is delegated to a dummy Dovecot server which is

*only* used for authentication (i.e. it doesn't provide IMAP or POP

storage). Username/password pairs are deployed by [ud-ldap](howto/ldap) into

`/etc/dovecot/private/mail-passwords`.

how is this thing built, basically? -->

TODO: some interesting "best practices" notes: https://bridge.grumpy-troll.org/2020/07/small-mailserver-bcp/

The LDAP server stores those passwords in a `mailPassword` field and

the web interface is used to modify those passwords. Passwords are

(currently) encrypted with a salted MD5 hash because of compatibility

problems between the Perl/ud-ldap implementation and Dovecot which

haven't been resolved yet.

## Issues

Project is coordinated in [ticket #30608][].

There is no issue tracker specifically for this project, [File][] or

[search][] for issues in the [team issue tracker][search].

When reporting email issues, do mind the [reporting email problems](doc/reporting-email-problems)

documentation.

 [File]: https://gitlab.torproject.org/tpo/tpa/team/-/issues/new

 [search]: https://gitlab.torproject.org/tpo/tpa/team/-/issues

Project was coordinated and launched in [ticket #30608][].

## Maintainer, users, and upstream

This service is mostly written as a set of Puppet manifests. It was

## Monitoring and testing

TODO: nagios monitoring?

To test delivery, make sure you have an `emailPassword` set

(e.g. through [update.cgi](https://db.torproject.org/update.cgi)). Then you should be able to use the

[swaks](https://tracker.debian.org/swaks) to test delivery.

change might be overwritten fairly quickly). Note that [other schemes

can be used as well](https://doc.dovecot.org/configuration_manual/authentication/password_schemes/).

We do not have end to end delivery monitoring just yet, that is part

of the [improve mail services milestone](https://gitlab.torproject.org/groups/tpo/tpa/-/milestones/4), specifically [issue

40494](https://gitlab.torproject.org/tpo/tpa/team/-/issues/40494).

## Logs and metrics

The submission server is monitored like other mail servers that have