Option to auto-archive email (sent or received by mail server) for some select users

An optional ARS that specifies which users mail should be auto-archived by the mail server. Mail sent by or received for a BBS user would be saved in .eml format, one message per file. When a user meeting the ARS sends a single mail message to multiple remote recipients, just one copy/file is saved. When receiving a mail message for multiple local recipients that meet the ARS, multiple copies/files would be saved.

The rationale is that some users mail sent or received by the Synchronet mail server should always be retained (in a format easily readable by most mail readers) until manually cleaned up, likely never (but it'd be trivial to write a script or program to auto-delete old archive files if desired).

Ideas for storage:

• data/user/<user-num>/<msg-num>.eml - already cleaned up by new user process
• data/mail/<user-num>/<msg-num>.eml - seems to imply that it's all the mail by/for the user, but it would not be - just the mail gone through the mail server