List Flag: filter-auto

Silently discards any submission that appears to be an automatically
generated reply, such as those generated by programs like the
"vacation" UNIX utility.

Listmanager will determine that a submission appears to be automatically
generated if it (a) has no "To:" header, (b) has an "Auto-Submitted:"
header, or (c) has a "Precedence: junk" header.  The former two cases are
a known behaviour pattern of programs like "vacation", and the latter is
in the draft Internet standards phase.