When someone in a company agrees on a meeting in their office with someone from outside the company, and the visitor arrives at time well-dressed and is rejected by the companies security without any explanation, then who is at fault? It is not the visitor, it is the awful cooperation between the person in the company and their companies security.
It is entirely reasonable to show how you've handed your mail to gmail and they refused it without actionable explanation, so it is a problem between the recipient and gmail.