Emails from a particular source fail to arrive

[#1]

Actually I am trying to recover my password from another forum. I am advised that an email is being sent but it never arrives on my computer.. I have white- listed the sender, and as well as looking my Thunderbird In Box  have checked PN's web mail IN and Spam. Catch All is on .
Can some one suggest what may be the problem and any thing I can do to ensure receipt?

[#2]

Not a lot, I had this with Navman and Bob did a test and he couldnt find his test e-mail, even contacted Navman and they blaimed it on the message company, never did get mail password and had to open a new account, the main problem was that the account used  PN as a part of the sign on