Are apostrophes valid in an email address?

[IvorW]

I've had a mailman subscription request from an email address that looks like this:

paddy.o'hagan at foobar.org         (this is not the real address; the domain has been changed to protect the innocent from spam)
I've had a dig through google and haven't found any comprehensive definition of what is a valid list of characters. It occurs to me that a single quote could b0rk a number of poorly written CGI scripts and be rejected by the more secure ones. The spamex.com/xemaps.com DEA service rejects it as being an invalid email address.

The pending moerator request has come through to me, so mailman clearly thinks the address is valid.

Who's right?

Ivor.