Welcome to the forums! 🙂
Hopefully someone here will be able to assist you more with this, personally I would not use gmail or yahoo so would be fairly unfamiliar, but I have found the Gmail help page here, so that be be of some use to your hopefully!
What exactly is happening with the emails?
When sending an email to your @gmail or @yahoo mailboxes, is there a bounceback error message popping up on the sender address at all? This will help figure out where the problem is coming from.