Another point that has been brought up by our vB tech is that some email services ( gMail is an example) have prefiltering of email. If you are using a client like OUTLOOK or THUNDERBIRD, these prefiltered emails are not downloaded. You would have to log into your web interface and check the junk folder, then mark them as "not junk" in order for them to start coming to your client.
While this may not be your issue, Harry does bring up a valid extra point in the troubleshooting process.