I set up my site with email verification, and afterwards a person signing up with an email account on the same domain as my site would receive the verification email. However, if the person was signing up with a gmail address, they would not receive the verification email. This was tested with a number of gmail addresses with the same result. (they are not going into the spam folder either, they just don't show up)
This is with the SMTP setting on or off. It does the exact same thing either way.
Does this sound like an SMTP problem on my host?