Let amavis bounce emails with banned content

iRedMail's questionable default behavior is to discard these messages
silently.

Warn about skipping releases when upgrading

Specify how to handle `config` file when updating

Set explicit version of phusion/baseimage

Add fix for logrotate error

Refs #1808

Update mysql's debian.cnf file

Update iRedMail to 0.9.4

Implement first version