mail-expire is a small utility which only purpose is to help on keeping the
size of multiple mail folders as small as needed (by removing outdated
messages).

Maildir and Mailbox formats are supported for input, both types are mentioned
interchangeably in this manual page. Output goes to Mailbox files.

The old messages are compressed with gzip or xz and stored in the file with
the name following the pattern MBOXNAME.MONTH_YEAR.gz (or similar).  The
reference time for the output filename is calculated from the current time
minus number of days specified in the first parameter.