MX record and PTR questions

[Mark Andrews]

> Hi there, something always bugged me with MX records.
> 
> In most domain setup examples we see an mx record setup such as
> (and forgive the exact syntax - this is just an example)
> 
> domain.com.au  MX 10  mail.domain.com.au
> mail A 202.123.456.789
> 
> My question is - does the name "mail" have any significance at all or
> is just an alias that is resolved by the A record. If  my server was
> called server1 (or fred or whatever) could I still set it up as:
> 
> domain.com.au  MX 10  mail.domain.com.au
> mail A 202.123.456.789
> server1 A 202.123.456.789 ; is this record even needed????
> 
> or would it be best to set it up as
> 
> domain.com.au  MX 10  server1.domain.com.au
> server1 A 202.123.456.789

	With only one MX record it really doesn't matter.  When you
	have multiple MX records, especially for the higher preference
	servers, having the name in the MX record match what the
	MTA thinks its name is important.  By default the MTA will
	get its name from the hostname/uname.

	Backup MTAs have to trim all MX records from the MX RRset
	which have the same or higher preference as itself before
	determining where to send the email.  If it fails to do
	this you get mail loops which may or may not be detected by
	the MTA.
 
> Also if my server was called server1 - would the reverse PTR have to
> read server1.domain.com.au or the name specified in the MX record (in
> the first case mail.domaim.com.au)
> 
> Hope someone can set me straight.
> 
> Cheers
> Wally
> 
> 
--
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: Mark_Andrews at isc.org