What do I add to the regex string so that only specific email domains will be accepted when registering new users?

My client in this case, deals with different colleges and only employees from these places are allowed to register on their DNN website.

To reduce workload on the site admin, they want to have users to be able to register themselves, but to prevent any unwanted users, they want the DNN site to verify the email domain names, simply by only allowing specific domains to be accepted upon registration.

I tried different things with the regex expression, but im not familiar AT ALL with regex and what I can google up doesn't work for me.....because I don't fully understand how the syntax work. :-/

But im under the impression that I shd be able to add something to the validation like a list (
@firstdomain.com | @seconddomain.com | @thirddomain.com) and so on and so forth which will result in the verification accepting any email which contains either one of those strings?


If so, how do I do it?

Cheers
Jake