Dissallow username that contains 'X'
 

Is it possible to set up filters to disallow the registration of username containing X, Y, Z,....n?

you can censor words that are used in username in vboptions

Would those same words also be censored in forum posts?

I am looking for something that would only censor it in usernames

AdminCP >> vBulletin Options >> vBulletin Options >> User Registration Options >> Illegal User Names ;)

Thanx!

On a similar note, is it possible to ban users based upon their email domain?

you can search out all users with a particular email domain and move them into the banned usergroup. afterthat, disallow new registrations from anyone with that particular email domain.

And how can I do that?

AdminCP >> vBulletin Options >> vBulletin Options >> User Banning Options >> Banned Email Addresses ;)