🚀 go-pugleaf

> *Excerpts from ext.nn.comp.mail.sendmail: 22-Apr-89 Re: sendmail parsing*
> *questions Mark Sirota@uhura.cc.roc (855)*
> > That is not a legal RFC822 address, please consider using something
> > like "user%machine1@machine2.dom" instead.
> That is not a legal RFC822 address, either.  Please never recommend the
> use of '%' in addresses.
Pray tell, what's not legal about it?  Lots of characters are perfectly
legitimate in unquoted ``local-part''s (the part to the left of an ``@'' in an
RFC822 mailbox).

To summarize:
user@host1@host2        not RFC822-legal; dates from RFC733 (pre-1982) days
user%host1@host2        legal if host2 is registered in the capital-I Internet
<@host2:user@host1>     if both host1 and host2 are registered in the Internet,
OK as an envelope address but not RFC822
user <@host2:user@host1>        if both host1 and host2 are registered in the
Internet, legal RFC822

Notes:
(a) ``%'' is a perfectly legal character, according to RFC822, in an unquoted
local-part, as are letters [A-Za-z]or digits [0-9] or any of:
        !#$%&'*+-/=?^_`{|}~

(b) RFC822 requires that all ``@host'' names used in a route-addr be registered
(presumably with a domain parent or with the root administrator).  The ``%''
pseudo-routing character is often used to express routings to hosts that are not
so registered.  The existence of such routings is of no concern to the
correctness of an RFC822 address, since in the mailbox address
``local-part@domain'', only the given ``domain'' is supposed to attempt to
interpret the ``local-part'' text.

(c) RFC822, in something of a botch, requires that a mailbox address that uses a
route-addr contain some text (a ``phrase'') to the left of the route-addr
(which, indeed, is required to be surrounded by ``<>'').

Needless to say, the fine points in (b) and (c) are often not enforced.  Be
liberal in what you accept and strict about what you generate.

                Craig Everhart
                Andrew message system