Nullmailer creates loop by attempting to send mail to #@<>

[WilliamEdwards]

We have a few machines where /var/spool/nullmailer/failed/ regularly gets filled up with bogus mail. The 'To' address for the emails filling up /var/spool/nullmailer/failed/ is '#@<>' (without ''). I feel like this is the result of some kind of failed variable substitution, where '#' is supposed to be the local part and '<>' is supposed to be the domain. Is this a result of sending mail to an empty address perhaps?

Either way, /var/spool/nullmailer/failed/ fills up and the disk runs out of inodes, seemingly because of infinite retries by Nullmailer.

In a mailing list somewhere, I read '#@<>' is a 'special address', without any further explanation of why it'd be a special address. The ##postfix and ##exim folks don't know either.

Has anyone seen the same behaviour?

Nullmailer version: 2.1-7