Strange problem with postdrop command

[SupuS]

Hi all

I found strange message in my /var/log/apache2/error.log

postdrop: fatal: file /etc/postfix/main.cf: parameter setgid_group: unknown group name: postdrop
sendmail: warning: premature end-of-input on /usr/sbin/postdrop -r while reading input attribute name
sendmail: warning: command "/usr/sbin/postdrop -r" exited with status 1
sendmail: fatal: www-data(33): unable to execute /usr/sbin/postdrop -r: Success

Has anybody idea what does it mean? Google was not very helpfull :(

In my /etc/postfix/main.cf is not line with setgid_group or postdrop ..

My ispconfig box run for a long time and this message was not showed before ... should I be afraid?

Thanx for any response ..

[till]

Do you have a group called postdrop in /etc/group ?

[SupuS]

Hi till

Thank you for replay.

Yes I have ..

postdrop:x:114:

[till]

Ok, thats fine. Please add the line:

setgid_group = postdrop

to /etc/postfix/main.cf and restart postfix.

[SupuS]

Done .. But still I have no idea why system works without this message for months and suddenly I get warning. Should I put this line to my other ispconfig boxes?
Anyway thank you for solution.