On Fri, 2011-08-26 at 13:10 -0400, Simon Brereton wrote:
mail:~# ls /var/spool/mail/virtual/domain.net/simon/new/ -rwxrwx--- 1 postfix mailsystem 2.5K Aug 26 03:33 1314326000.V801I1666018M803015.mail.net,S=2461:2, -rwxrwx--- 1 postfix mailsystem 2.5K Aug 26 03:36 1314326209.V801I1666019M447273.mail.net,S=2460:2, -rw-rw---- 1 postfix mailsystem 2.5K Aug 26 04:00 1314327630.V801I166601aM308173.mail.net,S=2477:2, -rw------- 1 postfix mailsystem 2.5K Aug 26 04:22 1314328966.V801I166601bM756462.mail.net,S=2461:2, -rw------- 1 postfix mailsystem 1.1K Aug 26 16:28 1314372534.V801I166601cM615258.mail.net,S=1097:2, -rw------- 1 postfix mailsystem 1.1K Aug 26 16:31 1314372685.V801I166601dM264242.mail.net,S=1097:2,
Mails are being delivered with 0600 permissions and not 0660 (the mails from courier seem to have all been 0770 as you can see). If I manually change the permission (to 0660) then I can see the mail in the MUA.
If /var/spool/mail/virtual/domain.net/simon has 0770 permissions, the new mails should be delivered with 0660 permissions. (I don't remember if having g+s makes any difference in the directory like you have in the domain dir.)
In any case, it would be better if mails were delivered as mailsystem:mailsystem 0600 since that's what you're reading them as. Unless you have some other good reason for requiring mailsystem group to be able to read them.