I've just finished searching the IETF's RFC 822 (email message format standard) and cannot find a definitive list of what characters are and are not valid for email addresses.

I know that alphanumerics, underscores, and hyphens are valid in email addresses. I've tried searching for programming routines to determine valid email addresses, but I was unable to find one that contained the ampersand (&) character.

I thought that ampersands in email addresses were not RFC 822 compliant, and verified this by attempting to sign up for a number of free email services with entirely valid email addresses except for the addition of an ampersand. None works.

I need to find a reliable document that spells out in black and white what characters are and are not RFC 822 compliant in the prefix (i.e., before the @) portion of an internet email address.