Bug#994289: fail2ban: On start and stop, emails go to root@localhost like it was on Debian 10, but also to nonexistant addresses set and escape:

[Mike Gerber]

Hi Olaf,

I can't confirm this on my systems, and I suspect that your mail command 
is something that doesn't understand "-E 'set escape'". Could you check 
what your mail command points to?

Here it is bsd-mailx:

# ls -l /usr/bin/mail lrwxrwxrwx 1 root root 22 Aug  4  2012 
/usr/bin/mail -> /etc/alternatives/mail
# ls -l /etc/alternatives/mail
lrwxrwxrwx 1 root root 18 Aug  4  2012 /etc/alternatives/mail -> 
/usr/bin/bsd-mailx

Cheers,
Mike