Monitor WhisperBack SMTP relays

We should monitor WhisperBack SMTP relays, e.g. using Nagios. We already monitor 1. whether the WhisperBack SMTP relay is up and answers SMTP commands; 2. whether the WhisperBack SMTP relay has email queued for delivery.

What’s left to do is an end-to-end test of the entire system, which is hard to implement.

Subtasks

#12086 (closed)

Related issues

Related to #12085 (closed)

Original created by @tails on 5729 (Redmine)

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information