Part of the problem is that RFC821 and RFC822 were designed to be
used in situations other than your standard Internet email (though
they're supposed to apply there as well).  So depending on the
context in which they apply there may  be more stringent restrictions
on the syntax of addresses and the like.

Another issue is that some aspects of RFCs 821 and 822 have been
modified since they were first proposed.  Thus although I rely on
those two standards for quick reference for any serious endeavour I
also look at the relevent parts of RFC 1123, which lays out the
application and support requirements for a great number of protocals
(including SMTP) and makes some modifications to them.

The syntax of a legal Internet hostname was first laid out in RFC
952.  1123 modifies this slightly in that it allows the first
character of a hostname to be either a letter or a digit.

To save you hunting through RFC 1123, the syntax specification for
localpart remains unchanged.

I hope this is helpful.

Thanks,
--
Jacob Haller, Technical Support
L-Soft international, Inc
http://www.lsoft.com/