Infrastructure

This issue is about refactoring the main mail server. Possible improvements include:

Base system:
* Upgrade to Debian 10

Dovecot (IMAP):
* Change mail storage format from maildir to mdbox, possibly compressed

Postfix (SMTP):
* Replace amavis by rspamd

amavis
* consider setting Postfix' @notify_classes@ to empty
* -switch switch to Milter- Milter
* Guilhem proposed to use systemd
<pre>
Assuming you're using systemd as PID 1, a
quick and dirty fix would be to tell it to auto restart the service.
Rather than editing the unit file shipped by the package (which would be
overridden by the next amavis update), I'd go for an override
systemd.unit(5) file instead:

$ mkdir /etc/systemd/system/amavis.service.d
$ tee /etc/systemd/system/amavis.service.d/override.conf <<- EOF
[Service]
RestartSec=1min
Restart=always
#Restart=on-abnormal might be more appropriate, see
#systemd.service(5) for details
EOF
$ systemctl daemon-reload
$ systemctl restart amavis

You can see if the override systemd.unit(5) file is taken into account
with `sudo systemctl show amavis.service | grep ^Restart`.
</pre>

hostmaster alias
* consider switching to local mailbox only in case of too many notifications

domains
* switch to DNSSEC and TLSA records if feasible