I have a mail server configuration based on Postfix for the smtp, Dovecot for the imap and virtual users receiving e-mails in maildir boxes.

I am also using Amavis and Spamassassin for content filtering.

I am not going now to describe this configuration, I think there are already a lot of very good tutorials about it all over the web. Moreover, the openSUSE maintainers made such a configuration quite easy : a sensible part of the work just consists in commenting out some line in the configuration files.

However, with the basic setup, I had an issue with permissions :  all e-mails delivered by Postfix were created with permissions set to 600.

A typical use case with which I got into trouble was spam learning, done with a cron script with a dedicated account (“vscan”, you don’t want to execute such a script with root, right ?).

In that case, what I need is files to be created with permissions 660.

It seems easy and rather obvious at first, but actually there is not such a setting in Postfix.

Actually, it is not really the job of the MTA to do it, so in the case of Postfix it doesn’t bother with the transmission of such a parameter.
Then, I tried to use Procmail and set UMASK in /etc/procmailrc, but this just didn’t have any effect.

After searching and trying in vain a couple of hours, I found out that Dovecot can also deliver e-mails from the MTA to the maildir with Dovecot LDA.

So I tested it out. The configuration is pretty straightforward.

Add the line in bold to the virtual user configuration in /etc/postfix/main.cf :

[...]
virtual_mailbox_domains = domain.com
virtual_mailbox_maps = hash:/etc/postfix/vmailbox
virtual_mailbox_base = /home/vmail
virtual_minimum_uid = 100
virtual_gid_maps = static:1002
virtual_uid_maps = static:1001
virtual_transport = dovecot
[...]

Now, add these lines in /etc/postfix/master.cf :

[...]
# Dovecot LDA
dovecot   unix  -       n       n       -       -       pipe
   flags=DRhu user=vmail argv=/usr/lib/dovecot/deliver -d ${recipient}
[...]

Finally, configure /etc/dovecot/dovecot.conf with these sections :

[...]
protocol lda {
  # If you wish to use plugins you need to specify plugin directory
  # For example quota enforcing is implemented by plugin
  module_dir = /usr/lib/dovecot/modules/lda
  # Address from LDA should send MDNs like out of quota
  postmaster_address = postmaster@domain.com
  # UNIX socket path to master authentication server to find users.
  auth_socket_path = /var/run/dovecot/auth-master
}
[...]
auth default {
[...]
  socket listen {
	master {
		# Master socket provides access to userdb information. It's typically
		# used to give Dovecot's local delivery agent access to userdb so it
		# can find mailbox locations.
	      	path = /var/run/dovecot/auth-master
      		mode = 0660
		user = vmail
		group = vmail
	}
	client {
		# The client socket is generally safe to export to everyone. Typical use
		# is to export it to your SMTP server so it can do SMTP AUTH lookups
		# using it.
		path = /var/run/dovecot/auth-client
		mode = 0660
	}
  }
}
[...]

And that’s all !
Restart Postfix and Dovecot, check the log to ensure that everything works fine.
Now all new mails should come out in the maildir folder with permissions set to 660.

Definitely, in my opinion, Dovecot LDA is the way to go : simple and extensible. Good bye Procmail and your cluttered configuration file.