Check registered email against values in another database

[jaffa123]

Thanks kh99, vBulletin seems complicated!

Could you define a 'bad email address' as one that doesn't exist in database A therefore cannot be added to database B?

In answer to your last question, the problem here is that not all email addresses will be from the same domain. A user could have registered on the wordpress site using an email.

Thank you for your reply, I can't figure this out though. Need to think it through again.