Restrict Email Domain for guests

Hi,

First of all, thank you for this great plugin.

My question is about restricting email domains at comment form for guests: to make a whitelist with email domains that users can use to comment. In other words, I want to restrict the posting of any comments unless they have a specific email domain.

I know I could do this for register users restricting the domain of their registration email, but I would like to do the same for guests. Is this possible?

Thank you in advance.