🚀 go-pugleaf

utterbac@husc10.harvard.edu (Brian (Margot?) Utterback) writes:
 > Recently, I contacted a workstation vendor about the mail system
 > that comes with the workstation.  The operating system is based
 > on System V release 4.  The mail system failed when the host portion
 > of an address was an alias or nickname.  The response was that 
 > RFC821 and RFC822 specify that the address must be the official
 > domain name and that the entries in the host file and any 
 > cname records in the DNS are irrelevent.
 > 
 > This seems a little farfetched to me.  First, the rfcs in theis
 > case seem to be irrelevent.  Don't they only specify what would
 > be in the headers, not the address given to the mailer?

RFC 821 (the SMTP protocol spec) definitely specifies addresses
that are to be given to the mailer.

Also, specific RFC 822 headers are used to generate reply
addresses, and these addresses are the ones given to the mailer.
So the addresses in the headers must be acceptable to the
transport system.

 > Second, why limit the address even in the header? You get the
 > host portion, ask the DNS what the MX record is.  It will
 > respond with the IP address and the canonical name.  Bingo,
 > you have the official name, just use that in the rest of the
 > processing.

Not quite.  If CNAME's were allowed for mail then you'd have to
do an extra lookup.  One lookup to map the aliases to the
canonical name, and another lookup for any MX records for the
canonical name.

For mail, MXs are the way to alias host names.  For everything
else use CNAMEs.  If you need both, then use both.