I have a VPS running Debian 8 in which I used this tutorial to set up. It is running dovecot and postfix. Recently I have started receiving errors every few minutes in my mail.err log file which look like this:postfix/pipe[4274]: fatal: get_service_attr: unknown group: vmailAdditionally, mail will not receive or send. It is all being backed up in the queue.I have no idea where to go from here. I have checked that both the vmail user and group exist and have no conflicting IDs, I have even removed them and re-added them, but I cannot find out what is causing this error. I have tried re-installing postfix and dovecot with no success, and Google was of no help. Any ideas?
postfix - unknown group: vmail
debian;postfix;dovecot
Found out that /etc/group was not world readable. I must have accidentally overwritten the permissions somehow. I used chmod 644 on /etc/group and /etc/passwd and that fixed it :)See: http://liveforcode.net/2015/08/27/solution-postfix-unknown-group/