My postfix configuration allows mail via several local_recipient_maps. However, delivery to "proxy:unix:passwd.byname" is specifically disabled. This normally prevents delivery to local unix users:
$ getent passwd | grep www-data
www-data:x:33:33:www-data:/var/www:/bin/sh
$ nc localhost 25
220 my.mail.host ESMTP Postfix
helo localhost
250 my.mail.host
mail from:[email protected]
250 2.1.0 Ok
rcpt to:[email protected]
550 5.1.1 <[email protected]>: Recipient address rejected: User unknown in local recipient table
rcpt to:www-data
550 5.1.1 <www-data>: Recipient address rejected: User unknown in local recipient table
However this morning I noticed an email delivered to the local www-data mail spool file. Looking within, I see that:
- It was a message from [email protected], sent by a different host within our network, using my.mail.host as the smarthost
- It remained within my.mail.host queue for several days while attempting retries
- It then bounced
- The bounce was delivered to a "www-data" mail spool file on my.mail.host
So my question is: why did this happen, and how do I prevent it from happening in the future?