To fpeter:
If you split the field it will violate the K.I.S.S. rule and about 40% (or more) of the real people who fill out the form will do it wrong. If it is important to you to receive messages from your web site visitors I strongly suggest that you do not use a split field.
Even the "brightest and best" Web Pro World forum members often misread a thread and then post answers that aren't pertinent to the question............think of what having to actually read and think would do to the average person trying to fill out your form??????
I tried several things with forms and form validation methods, none of which were satisfactory - so I finally made a graphic with my email address on it which people have to read and type into their own email to contact me. It actually works.
The graphic is complicated enough that the spam bots can't decode it and read my email address, but easy for real people to read. See it here:
Happy Day Cards CONTACT ME Page
Have a good day!