I would make a guess that this is (was) the problem.
Code:
Aug 15 22:22:34 lespaul saslauthd[23727]: auth_zimbra: royngan@imocha.com.my auth failed: curl_easy_perform: error(6): Couldn't resolve host 'lespaul.imocha.com.my'
For some reason your server became 'invisible' ie it's address couldn't be resolved. Do you run a DNS server or lose your connection to a DNS server at that time? Did other things start to fail? How did you recover, a reboot?