I am relaying email from my webservers to Zimbra using Postfix. Whenever large amounts of emails are sent at the same time from one of my webservers the connections to my Zimbra server are timing out and the emails in the mail queue on my webserver are deferred.
Here is an example of a timeout message from the mail log on one of my webservers:
While these emails are sitting in the Postfix queue on my webserver as deferred relaying an individual email from my webserver to Zimbra sends without timing out.
postfix/smtp: 4404C50587: to=<email@example.com>, relay=none, delay=12769, delays=12748/0.03/21/0, dsn=4.4.1, status=deferred (connect to zimbraserver.com[zimbra-ip-address]:25: Connection timed out)
This leads me to believe that the issues lie with Zimbra accepting relaying of large numbers of emails at the same time.
I am unable to find any errors on the Zimbra server so I don't know what is causing this.
Please if anyone has experienced this before or can give me some pointers on where to look/ what configurations to change your suggestions will be much appreciated.