Restricting registration to certain types of email address

[fallen_angel]

SMF Version: SMF 1.0.7
Is it possible to restrict registration to certain types of email address? The scenario I'm looking at is setting up a board for medical personnel. I've been trying to work out how I could ensure that they are genuine medical personnel without requiring their employers to provide written confirmation <hehe> and figured the best way to do it would be to only let people with a "medical" email address register, for example here in the UK NHS staff have email addresses that end in .nhs.uk. Is it possible to do this, and any ideas about how I could go about setting this up? I'm guessing if this is possible it would be somewhere in "Register.php", but I'm not really sure where to start looking. Any advice appreciated.

TIA