I've done a lot of searching around an ongoing issue and I was hoping someone could help me.
I've been running Zimbra NE (Starter Licencse) for 4 years in our SME (14 mailboxes). It's running as a VM on VMWare ESXi and the VM has all the recommended resources allocated to it.
We route our mail in via a SPAM filter at our ISP, mainly for some resilience in the case our network connection goes down. The MX record for <mydomain>.com points to the spam cluster and the ISP then sends on to Zimbra over smtp. Our fire wall has 25/465/587 routed to the zimbra box (which is called <myco>-zcs0.london.<mydomain>.com). I've set a wild card Inbound SMTP name for *.<my ISP's domain>.co.uk.
About a month ago we started to experience a delay in receiving some mail. Outgoing mail is transmitted OK and incoming is received OK about 60% of the time. In the case it doesn't come in OK, it's queued at our ISP and they try again after about an hour or so (although this retry time seems to vary from 5 mins to 12 hours). Given we have no issues with internal mail and that in general traffic is flowing in and out to the internet, I am satisfied that our config is sound.
Checking /var/log/zimbra.log I see traffic coming in but then occasionally we get an error:
I have other entries in zimbra.log showing correct delivery of spam8.<my isp>.co.uk
Apr 16 14:55:07 <my-server-name> postfix/smtpd: connect from spam8.<my isp>.co.uk[<IP adress>]
Apr 16 14:55:07 <my-server-name> postfix/smtpd: lost connection after CONNECT from spam8.<my isp>.co.uk[<IP adress>]
Apr 16 14:55:07 <my-server-name> postfix/smtpd: disconnect from spam8.<my isp>.co.uk[<IP adress>]
I've tried reboots, updates, using alternate internet connections but nothing seems to resolve this.
Any thoughts gratefully received!
Zimbra Network Ed. 8.0.7 Ubuntu 12.07 x64