Consider voting for these ideas related to non-standard characters in an email address.  I did not know until today that you cannot use the underscore character in a salesforce email field, but it's a problem for sure.  If it hasn't hit you yet, it will (or you just haven't seen the error yet).

https://success.salesforce.com/ideaView?id=08730000000Z5bLAAS

https://success.salesforce.com/ideaview?id=08730000000GsDZAA0

@Admin Group, Raleigh, US @Solo Admins @* Salesforce Administrators *