Re: Newbie to Exchange needs MX record info

The help file that comes with Exchange would be appropriate. Search SMTP and
or Internet.

MX records are not "required" per se to deliver mail per RFC. However, it is
a best practice to have one that designates the mail handler for your
domain. This is accomplished by designating a host as a mail handler (MX is
the designation for mail handler in DNS terms.)

It is a best practice to designate a MX record that specifies a host by it's
A record vs. any other type of record. During a SMTP transaction, the MTA
(mail transfer agent) will receive a message. It will determine where to
deliver that message and if it determines that message to be a remote MTA,
it will then look at it's routing table to figure out if it knows how to
contact that responsible MTA. If it doesn't have a specific route, it will
then look to DNS and specifically will look for a MX record that specifies
the mail handler for that domain (domain here is everything to the right of
"@" in the address.) If an MX record does not exist, the MTA will look for
an A record. If that doesn't exist, it will fail the delivery and return a
non-delivery receipt (NDR). If an MX record does exist, it should reference
an A record. Once that A record is discovered, it will be queried for it's
IP address and a conversation will be started between the MTA's via the well
known SMTP port, TCP 25. Messages will then be transferred and the recipient
MTA will become responsible for the next step of delivery.

Basically, that's how it works. Daniel Petri seems to have taken the time
to explain it as well.
http://www.petri.co.il/configure_mx_records_for_incoming_smtp_email_traffic.htm

Having more than one MX record is done because the way SMTP mail works, it
will try the lowest weighted (preferred) mail handler first. If it receives
an error (depends on the error type), the sending MTA should then try to
send to the next mailer listed. This provides some level of failure
tolerance because you can have multiple hosts that receive mail for your
domain. Should one be out of service, the other should pick up the slack.
It's not a requirement.

Typically, your ISP will offer queuing services. If your host should be
down, they'll accept mail for your domain until you come back on-line at
which time they'll dump the queued messages to your mailer. So in practice,
you'll often see records that look like:

yourdomain.net MX preference = 10, mail exchanger = smtp.yourdomain.net
yourdomain.net MX preference = 50, mail exchanger = SMTP.yourISP.net

Which would typically send mail destined for your domain to
smtp.yourdomain.net. However, if that server were unavailable, a sending
host would try to send the mail to the other server, SMTP.yourISP.net. When
smtp.yourdomain.net came back into service, it would then receive the queued
messages from the ISP MTA, SMTP.yourISP.net.

One caveat to be aware of, is that some admins have configured their hosts
to look for reverse DNS records as a way to reduce spam. I don't consider
this effective, but that's my opinion. The reason I don't, is because I can
have a sending host that is not also a receiving a host and therefore I
wouldn't have a corresponding MX record. To have the sending and receiving
host be the same, is more often done in smaller IT shops vs. the larger and
global shops. By RFC, I am not required to have an MX record for a host that
is sending only nor would I want to as there would be no path for that mail
handler to ever deliver a message. A PTR record is a good idea for your
sending host for the same reason. While not required, it is a good idea to
more reliably transfer messages with your customers because some hosts are
configured to check for a reverse lookup when receiving a message from your
domain. Same goes with SPF records (you may want one); I don't spf records
as effective nor desirable, but what do I know? ;)


Does that help?

Al



"Gary Demi" <GaryDemi@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message
news:1067F097-FA48-4B5F-97D3-5F0957549B12@xxxxxxxxxxxxxxxx
>I thought two MX records where required. The MX records should read
>something
> liklike mail.yourdomain.com or smtp.yourdomain.com (what prefix does
> Exchange
> use, and what help file are you referring to?
>
> Thanks
> --
> Gary Demi
> Software & Communication Concepts, Inc.
> Microsoft Registered Partner
> Houston, & Phoenix
>
>
>
> "Al Mulnick" wrote:
>
>> Two MX resource records?
>>
>> MX resource records are used to designate mail handlers for your domain.
>> The A RR is the host name, and the MX references the A.
>>
>> If you have the A already, you would have your lowest priority MX record
>> specify the A record as the mail handler. You may also want a reverse
>> PTR
>> (some domains check this record when receiving mail from you), but that's
>> up
>> to you. The higher priority record, if you specify one, would typically
>> be
>> for a backup mail handler such as might be provided by your ISP.
>>
>> Check out the help files for more information regarding MX and A records
>> and
>> how to set this up. I believe it has mail flow pictures in there if
>> that's
>> helpful.
>>
>> Al
>>
>>
>> "Gary Demi" <GaryDemi@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message
>> news:9DEFC442-1929-4252-A261-BE4FFCA4A901@xxxxxxxxxxxxxxxx
>> > We are running SBS2003 premium and starting to use exchange. Right now
>> > we
>> > are
>> > running one NIC behind a NAT router.
>> >
>> > We have access to the DNS records on out nameserver through ouw domain
>> > registrar.
>> >
>> > We have a public domain name pointing to the SBS2003 computer (via the
>> > A
>> > record). To what URL do we point the two MX records (pri=0 & pri-10)
>> > so
>> > that
>> > Exchange Server is recognized as a mail server.
>> >
>> > A link to the the appropriate setup docs would be nice.
>> > --
>> > Gary Demi
>> > Software & Communication Concepts, Inc.
>> > Microsoft Registered Partner
>> > Houston, & Phoenix
>> >
>>
>>
>>


.

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