Timo, in response to Hadi, wrote:

...

Apr 24 20:25:46 lda(jamal@example.com): Fatal: setgid(5000(vmail) from userdb lo okup) failed with euid=8(mail), gid=12(mail), egid=12(mail): Operation not permi tted (This binary should probably be called with process group set to 5000(vmail ) instead of 12(mail))

Configure your MTA to run dovecot-lda as vmail instead of as mail.

Yeah, what he said. Someone helpfully added documentation on how to do this at the end of Dovecot1's wiki (http://wiki.dovecot.org/LDA/Sendmail), which probably should be copied to Dovecot 2's wiki. So that's what I did.

Joseph Tam <jtam.home@gmail.com>