I am making a simple mailing list script.

I have a table in 1 database called "newsletter", with a column called "email" which contains the newsletter sign ups. I also have a table in another database called "user" with a column also called "email" with the users email addresses from my forums.

Now, I have a question :

How would I go about in the sign up process of checking BOTH databases to check if the email address already exists, then displaying the appropriate message?