Cannot receive/send an email

[greysnipe]

Is there any issues when it comes to postfix?

Upon checking the zimbra.log, I've found the messages:
zimbratest postfix/error[23423]: 296B51C25FD: to=<user@domain.net>, relay=none, delay=282531, delays=282231/300/0/0.06, dsn=4.4.2, status=deferred (delivery temporarily suspended: conversation with zimbra.domain.com[192.168.100.79] timed out while receiving the initial server greeting)