It depends on the type of smtp used. As he has TLS enabled, he either needs 587 or 465.
@lpneblett believe me, I’ve wasted hours and hours on this, there’s not always logic.
Now I’ve seen that with my settings it works 100% and that’s okay
As the blurb above notes, you may not need to specify 465 as presumably the client will default to a port given a specific type, but it is recommended. We are all indicating how it works for us given our locales, but that does not necessarily mean that one method is universal to all others.
So, try none, 465 and 587.
exactly, probably adding the port becomes something like smtp.gmail.com:465:465
exactly as I noticed on the NAT if you add :5060 to the public ip