I have not forgotten in reporting back, after solving the issue in the firewall I have connection between the Kaseya server and the Exchange server but still I was not receiving emails.

After going through again the complete troubleshooting document:

The solution was to reinstall the SMTP service, now it is working fine.
Thank you very much for your help and I hope this post will help someone else in the same situation.

Great to hear, and thanks for getting back to us about this...

Sometimes it's the easiest thing

Legacy Forum Name: How-To,
Legacy Posted By Username: thirteentwenty