This might be a PEBKAC on my end, but in our old server, "vacation" responses would only be sent back to an origin address once per day because we had ":days 1" in the rule.

On the new server, even though we have ":days 1", pigeonhole is sending responses to every message, resulting in multiple vacation responses each day back to each origin address.

The following was generated by Roundcube's web interface, it looks to be correct.

require ["vacation"]; # rule:[vacation-reply] if allof (not header :contains "Subject" "[spam]", not exists "List-Unsubscribe") { vacation :days 1 :addresses ["email1@example.com","email2@example.com"] :subject "Out of office reply" text: I am currently out of the office July 11th and 12th, returning on July 15th.

During this time I will have no access to email.

Thank you.

User So-And-So . ; }

Interestingly, if I look at .dovecot.sieve.log, I see error messages like (except that the vacation responses are, in reality, being sent):

error: msgid=20130711134816.35B9A40335@mail.example.com: failed to send vacation response to originemail@example.com (refer to server log for more information).

And in the maillog:

Jul 11 09:48:17 servername sendmail[28244]: r6BDmHem028244: SYSERR(UID1132): Who are you? Jul 11 09:48:17 servername sendmail[28244]: r6BDmHem028244: Authentication-Warning: servername .example.com: Unknown UID 1132 set sender to <> using -f Jul 11 09:48:17 servername sendmail[28244]: r6BDmHem028244: from=<>, size=725, class=-60, nrcpts=1, msgid=dovecot-sieve-1373550497-202242-0@servername.example.com, relay=Unknown UID 1132@localhost

My guess at this point is that I've failed to configure pigeonhole and/or postfix's copy of the sendmail command properly so that it can create the "who I have send mail to recently" file.