So the deal is one of my clients was having an issue with messages not being delivered in their Exchange 2003 environment most of the time with the message. (Happening when sending to the same 5-10 domains, but fine otherwise.)
554 Denied (Mode: normal)
I contacted the other IT Dept and asked them to look into it on their end got the general response of "Not our problem".
So we used this as an excuse to rebuild the exchange server onto newer hardware...assuming the issue would be solved in the process...It was not.
We have now configured mail to go through our ISP's external SMTP connector instead just to root out issues of it being on our end...This has also not solved the issue.
I have searched around EE and tried a lot of the resolutions already listed but none have helped me so far.
I am sitting with angry customers who just want the issue resolved.
Thank you in advance.