A number of questions have come up about email error codes of the forms:
nnn (a 3 digit code)
and
n.n.n (3 digits sepatated by periods)

The first is an SMTP (Simple Mail Transfer Protocol) error code which is
defined by RFC0821, section 4.2.  See:
http://www.cis.ohio-state.edu/cgi-bin/rfc/rfc0821.html

The second is an enhanced status code that is defined and proposed (not yet
Standard) by RFC1893.  This RFC proposes to replace the SMTP codes and some
email systems have started to use them, usually reporting both.  See in
particular, section 3.
http://www.cis.ohio-state.edu/cgi-bin/rfc/rfc1893.html

A good source for RFC's and Internet standards (STD's) is:
http://www.cis.ohio-state.edu/cs/Services/rfc/rfc.html
and
http://www.ietf.org/rfc.html (the official repository for Internet
standards, others are "mirror" sites)

You might want to save some of these links in your Internet Explorer
"Favorites" folder for future reference.


Don Good