Using MX records to validate email addresses

I have a contact form on my web app, it gets alot of spam.
I am validating the format of email addresses loosely i.e. ^[email protected]+..+$
I am using a spam filtering service (defensio) but the spam scores returned are overlapping with valid messages. At a threshold of 0.4 some spam gets through and some customer’s questions are wrongly thrown in a log and an error displayed.

Generating confirmation code for an email confirmation

Using PHP, what are some ways to generate a random confirmation code that can be stored in a DB and be used for email confirmation? I can’t for the life of me think of a way to generate a unique number that can be generated from a user’s profile. That way I can use a function to make the number small enough to be included in the URL (see this link). Remember, the user has to click on the link to “confirm/activate” his/her account. If I can’t use numbers, I have no problems using both letters and numbers.