I'm not sure if this has been there, but I could have sworn it wasn't on the neomail I just sent. Now when you click to neomail someone, under their username in the neomail form it says whether or not you can neomail them.
Example:
To: fake_username
You should have no problem Neomailing that user.
Subject:
Message:
I think that's very cool and a great addition.
If this has already been posted on and I missed, it, I appologize, but I just noticed it.