PHP conditional email?

Hey all - I am looking to do the following. After my client adds a user to the database, he wants an email sent to them containing a welcome message, their userID and password. The only problem is that it cant be automated, because he approves them before they get added.

Here is what I need, I have a php form where he enters the newly added users email address. On ‘Submit’ if there is a match with the entered email, id like an email sent to the user containing the information that cooresponds with the email address in the mysql database (userName and userpass)

The mysql database already exists.

Please advise, thanks.!!