We are running zcs-NETWORK-7.1.1_GA_3196.RHEL5_64.20110527001604 with patch zcs-patch-7.1.1_GA_3222 applied. We have implemented a multi-server environment (one mail-store server, one LDAP server) and upgraded from version 6.0.12 two weeks ago. We have approx. 2800 users. We have experienced two alarming events. One manifested itself by our mail store not accepting any mail although you were able to log in using an IMAP client (happened during a "slower" time of day) and the other the mail store was accepting mail albeit very slowly and the Zimbra web interface was non-responsive ("busier" time of day). Each time, in the zimbra.log, the following message occurred over and over again responding to different pieces of mail:

Aug 16 09:50:01 norm postfix/error[27328]: 0829D1EA8B5: to=<abc@mail.uri.edu>,
relay=none, delay=0.09, delays=0.05/0/0/0.04, dsn=4.0.0, status=deferred (deliv
ery temporarily suspended: host charlie.uri.edu[131.128.1.96] refused to talk to
me: 421 charlie.uri.edu Zimbra LMTP server closing connection; service busy)

Our LMTP threads hit the upper limit each time and did not come back down until I restarted zmmailboxdctl.