[Feature]: Add “nullmailer” als allowed MTA for email notification

[raabf]

User story

Allow “nullmailer” as MTA and do not display an error message.

Game

No response

Linux distro

Debian 12, Debian 11, Ubuntu 20.04, Ubuntu 22.04, Ubuntu 24.04

Command

command: start

Further information

nullmailer is nice because it is a minimal MTA, just to send email out — and not more than this is needed by LinuxGSM.

I am using nullmailer with LinuxGSM already for some years now and it works fine.

However you get the error:

Missing dependencies: postfix Run: 'sudo apt update; sudo apt install postfix' as root to install missing dependencies.

although sendig emails by LinuxGSM works fine as the mail and mailx commands can use nullmailer as MTA.

See #4871 for a fix.