I had this too. Google decided to block my company's domain for no good reason. I also couldn't reach anyone in Google to sort it out - I eventually had a respo

I had this too. Google decided to block my company's domain for no good reason. I also couldn't reach anyone in Google to sort it out - I eventually had a response that "it's an automated system, there is noone who looks after it or can do anything about it". My company's email is hosted on GMail, and that also silently swallowed any in- or out-bound emails that as much as mentioned my domain. Including the email to our support inbox from our customer telling us they were having problems. Running anything in production at the whim of Google is too much of a risk, and I've been migrating everything I can off them ever since. They're a menace.