In SIMS Digest #1600, The Count of CipherSpace responded to rashantha de silva:
>[much stuff deleted]
>It would be more like:
>
>company1.com.          MX  10  mail.idealzone.net
>
>>and in my dns setting for idealzone.net change
>>
>>mail.idealzone.net.   A   new ip address
>
>Correct.
>
>And:
>
>mail.company1.com      A   new IP address

An "A" record for "mail.company1.com" is not necessary, unless oubound mail
is sent with a return path of "[EMAIL PROTECTED]"; if it goes out with
"[EMAIL PROTECTED]", the "MX" record pointing to "mail.idealzone.net" is
sufficient.


>or, you could set mail.company1.com as a CNAME to mail.idealzone.net
>(this way if you change IPs you will only need to change the A record for
>mail.idealzone.net).

DON'T do this.  The FQDN (fully-qualified domain name) that an MX record
points to (i.e., what's on the right side of "MX") should be an "A" entry;
_only_ use a CNAME if you take into account the "aliasing" that may (or may
not, depending on the client and intermediate MTAs) occur -- see 
RFC2821 (http://www.ietf.org/rfc/rfc2821.txt).

In short, using a CNAME as the Count suggested _may_ have the effect of
rewriting an original
   "To: [EMAIL PROTECTED]"

to
   "To: [EMAIL PROTECTED]",

which is probably _not_ what you want (and even if you _did_ want it, it
may or may not happen, dependent upon the _sending_ machine[s]).

Michael A. Pasek
Pasek Consulting, Inc.
9741 Foley Boulevard NW
Coon Rapids, MN  55433-5616
(612) 597-5977
[EMAIL PROTECTED]

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