address addresses browser call causing character characters checkout combination complain correctly customers e-mail email errors few non-standard page problem type valid validation version

I have had a few customers call me and complain that the email validation on the checkout page is coming up with errors. Most of these customers have a "." or a "-" or some other non-standard (though valid) character in their e-mail addresses. Quite often, when I type them in for them it goes through correctly.

Is there some combination of browser version <-> email address that might be causing the problem?

What characters are valid as far as e-junkie is concerned in an address?

Thanks