We have recently changed ISP’s as well as moving our DNS management to the new provider. We are running MS Exchange 2003 in house with a front end and back end server. During the migration to the new ISP we changed our MX record from a generic url to mail.domain.com. There was a delay in creating our RDNS and PTR records of a day or so.
Currently we have an issue with a receiving email from AOL and a couple of other domains. I will use AOL as our example. AOL subscribers are receiving bounced email with SMTP 4.4.7 delayed delivery. I have attempted the following to resolve the issue. Outgoing email is not affected.
Checked and verified correct virtual server settings on our front end server
Checked and verified using nslookup our MX and PTR records
I have checked our DNS records with online services such as DNSstuff.com, and mxtoolbox.
We are running GFI mailessentials, which initially was using a grey list feature which I have disabled. I have also added the AOL domain to our whitelist as a test.
The difficulty in solving this issue has been that the bounces are intermittent and only a small number of AOL subscribers are affected. It seems to be random in that email is delivered fine for a day or two then it begins to bounce.
Any information that can be provided to point me in the correct direction would be appreciated. I am thinking that it is a DNS issue and do not know where else to look.
Thank you in advance for your help.