After some research I found this way to validate an email:
RegexMatch(thisRow.To.ToText(),"\w+([\.-]?\w+)*@\w+([\.-]?\w+)*(\.\w{2,})+$")
Disclaimer:
It may not work for all proposes, but maybe the most common.
I found out that there are a lot expressions to validate emails and none of them work 100% so I suggest digging a little more