> They will not extend the 2FA tokens' lifetime, As they shouldn't. This will compromise the system's security. > and they will not decrease their mail server

> They will not extend the 2FA tokens' lifetime, As they shouldn't. This will compromise the system's security. > and they will not decrease their mail server retry period. Is their retry period not following the RFC? Graylisting has always required constant manual intervention when I managed mail servers. I'd say just whitelist their domain and move on. Another solution is to outsource spam filtering to some 3rd-party service that will forward emails to you. It might be well worth your time.