This reverts commit 1bc33d5d.

Nextcloud Mail is having issues with the following Dovecot error:
```
failed: Invalid quoted-printable input trailer: '=' not followed by two
hex digits
```
From
https://forums.cpanel.net/threads/dovecot-invalid-quoted-printable-input-trailer.648081/
it appears that some capabilities are missing. Add them.

We're reaching the limit frequently. Either because I have multiple
clients on the same machine or because I have even more clients on the
same network behind the same IP address.

Use the new names given by Docker Compose.

In the SpamAssassin learn script, avoid going over mailboxes that
haven't changed in 2 days (the learn job runs daily so it should cover
failures as well).

For nehe.sr.

I think that https://gitlab.com/gitlab-org/gitlab-runner/-/issues/1736
is solved and the version I have deployed has the fix.

Use the Docker snippet.

- Use an environment variable for setting the location of the dhparams
file.
- Don't generate the file if it already exists.
- Use the dhparams file in the host in production.

Basically, just what I did since the last commit. Includes the Exim4
SMTP server.