[Techtalk] kindergarten mail server question

[Raven, corporate courtesan]

Heya --

Quoth Carla and Kai:
> >Example: trusty Postfix server is all set up and configured at 
> >carlas.domain.com, ready to start work moving mail over the Internet. Well 
> >somewhere out there are DNS and MX thingies that have to be configured, 
> >right? Assume I can log into wherever to do all this. (in this case, my 
> >domain name registrar provides user DNS management.)

	Right.  I'm going to assume that you're using bind for your DNS
server -- most everybody does.  If you aren't and you'd rather have the
explanation in djbdns terms or Meta-IP terms, let me know.

	There are a bunch of different sorts of records that you should
care about.  The one you're asking about, the MX record, tells anyone
who asks your DNS server what the mail server(s) for your domain is
(are).  You can have more than one mail server if you want, but I'll
keep it simple since you only mentioned one.  So, all an MX record is is
"Mail server here!"

	You also need to know where "here" is.  So if you tell bind that
your MX server is at mail.carlas.domain.com, it needs to know what IP
address that is.  For this, you need an A record.  A records map names
to IP addresses.  There are also PTR records, which do the reverse and
map IP addresses to names.  The A records are in the zone for your
domain, and the PTR records are usually found in the in-addr.arpa zone.
Make sure that you have both of those in there for your new mail server.  

	Omitting the A record will cause "okay, I know the name of the
mail server, but not how to get to it, aaaaaaah!".  And DNS won't work
for that server.  Omitting the PTR record causes more subtle failures --
your users may have trouble subscribing to mailing lists (some mailing
list managers check the reverse lookup of the IP a subscription request
came from as a security feature), or using ssh or ftp to connect to the
box (depends on their configuration whether they try to do lookups for
that).

	There are also CNAME records, that are essentially aliases.
"fakeout.carlas.domain is the same machine as mail.carlas.domain", for
example.
 
>     MX  10   mail.carlas.domain.com
>     MX  20   carlas.friend.com
> 
> You can use any numbers you like for this, but your primary *must* have a 
> lower number than your secondary (and any tertiaries).

	Yah.  Like Kai said, the lowest number is the primary
(preferred) mail server.  If that one becomes unreachable, then the
secondary will be used.

	Hope that helps.  If you need more syntax help on how to set up
these records, just ask.

Cheers,
Raven 
 
"Just think of me as a very scary cricket."
  -- Louis, after the fearsome chirping noise my car was making turned
     out to be the metal plates on his jacket