Postfix Virtual Mailboxes and Procmail Filtering
For some time I’ve been running an ISP-grade e-mail hosting system on our server (it might be a bit of an overkill, I know), using Postfix, and Courier IMAP and Postgres as database backend. This is not the topic of this post, but followed this tutorial while setting it up and changed some MySQL-specific things to Postgres (BTE: postfix wiki article also discusses this topic).
The system works fine, but what’s been on my mind is how to enable server-side e-mail filters (rules, etc.). A simple example could be to deliver spam messages directly to “spam” folder, but other things could also be interesting (e.g. rule based filtering, autoreplying, folder sorting, etc.). All in all, what I was looking for is “procmail for virtual mailboxes”.
The most obvious option mailbox_command = /usr/bin/procmail in main.cf doesn’t work, because it only refers to local delivery (done using local, not virtual command). Looking into this matter a bit further, here are the possible soulutions I found on the web:
Change virtual delivery to local
In this case postfix should just work, however you need to make sure that it delivers mail to correct mailboxes (it’s not trivial). Also, if users have per-user procmail files, they can probably easily access each others mailboxes (essentially no file system-level permissions here).
This post and the followup discussion discuss this topic (in short, setting virtual_transport=local or virtual_transport=postfix is not such an easy solution).
There’s an interesting discussion here (check all the e-mails) and one post suggests virtual=local. Again, I’m not sure how well it works. Essentially, the problem is that procmail is not aware of users stored in the database.
Change virtual delivery to maildrop
Maildrop can connect to the database and check user account there (this option is supposedly not enabled in the debian package).
Links:
- Gentoo howto
- Virtual readme disusses how to setup Postfix to deliver some mail using maildrop.
- Postfix Maildrop Howto even more specific.
- Another howto on Debian
Use Courier’s MTA and procmail
This site briefly mentions how to enable it. Haven’t tried it.
To summarize, I think that the most reliable option is to use maildrop with database support. I will give it a try…
February 7th, 2006 at 1:35 am
[...] I decided to use maildrop (I discussed Postfix and procmail issues here) and followed this tutorial, with the following exceptions: [...]
April 11th, 2006 at 8:35 am
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June 6th, 2009 at 5:41 pm
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