I've a terrible problem with my production zimbra, this morning i've found in log this output like this
Jun 30 06:45:13 mail postfix/error: B81DA632FF1: to=<email@example.com>, relay=none, delay=18140, delays=18140/0.21/0/0.47, dsn=4.7.0, status=deferred (delivery temporarily suspended: host mx-tw.mail.gm0.yahoodns.net[220.127.116.11] refused to talk to me: 421 4.7.0 [TS01] Messages from X.Y.Z.T temporarily deferred due to user complaints - 18.104.22.168; see http://postmaster.yahoo.com/421-ts01.html)
Now the mail server has become (itself) Open Relay and now I've 20K email in queue..
This is in production for about 15 months without problem.
How could I solve ?
Thank you very much