WordPress MU

I would like to restrict signup to specific domains. I am aware that it is possible to restrict signups via Site Admin>Options. However, we prefix our domains; for example user.name@school1.ourdomain.com and user.name@school2.ourdomain.com . Other than added each of the 40 domain manually is there a wildcard command that I could use, for example *.ourdomain.com?

I just wanted to check this before I use the hack supplied by andrea_r on http://wpmututorials.com/hacks/how-to-moderate-signups/.

Have you tried putting "ourdomain.com" into the restrict email box?

Yea i tried that but it does not work, just says "Sorry, that email address is not allowed!".

Is the hack my best bet?

Please could someone advise me if I manually enter all our domain names (60 – 90 entries) into the “Limit Email Registration” could this cause problems else where within Wordpress or MySQL database in terms of performance?

Each of our school have different email adderss (e.g. school1.domainname.com, school2.domainname.com .....school89.domainname.com) and the blog servers is only for the use by approved schools.

I have the same set-up with over 180 domains entered and have had no problems.

Steve