Use LDAP to determine whether users receive mail

[mitchb]

We presently queue mail for locker@… when a locker isn't signed up for the mail_scripts service because the only way to determine that is to check for existence of /mit/locker/mail_scripts/procmailrc, and we could mistakenly conclude that the file doesn't exist and drop users' mail during an AFS issue.

We should modify our LDAP schema to store a boolean for whether a user should receive mail. We should default this to "false" for new accounts, and set it to "true" when a user runs signup-mail. For existing users, we should set it to "true" for anyone with a procmailrc and "false" for everyone else (unless they're specially handled in /etc/aliases or something). We should then either get Postfix or procmail to check this value and discard mail immediately if it's false.

This will alleviate much of our mail queue growth issue.

See the following zlogs for more discussion:

/mit/sipbzlog/scripts-by-instance/mail (Jun 25 2011) /mit/sipbzlog/scripts-by-instance/mailq[.d] (Jul 15 2011)