Has anyone found the way to change Email ValidationExpression yet?
I'm having the same problem now.....
The email filed doesn't accept "-" in the email address before @.

There is no email item in "Manage Profile Properties" edit.
I tried to modify the code in \controls\user.ascx, set the  regularexpressionvalidator enabled="false" but didn't change anything.

Thank you so much Charles, I was so glad when I saw your reply this morning. :D
I'm using DNN4.4.1 and with your help I found the RegularExpressionValidation String in UserInfo class in the Library, it is exactly as you post:

\b[a-zA-Z0-9._%-+']+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,4}\b

But it really doesn't accept email like kbc-a@mycompanyname.com

Maybe it's becasue of the "-" has special meaning in regular expression, so that is the only character in  [] that doesn't work, so I added a "\" in front of it as:

\b[a-zA-Z0-9._%\-+']+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,4}\b

And it works now!!