Hey Bruce,   Thank you for your response, I appreciate it and providing a reference link.   As for any rules, we have a few in-place but it's not blocking nor disrupting GMail SMTP services. I am pretty sure its the vendor's software that has the issues. I did open those ports on the client's side and no success either. Right now, I am waiting on the vendor to provide any IP addresses, CNAME or something I can add to our DNS records. ... View more