Do I really need an MX record? (for e-mail to work)

sm5w2 at hotmail.com sm5w2 at hotmail.com
Thu Dec 22 01:42:21 UTC 2005


MRJ InfoTech Admin wrote:

> The problems you will likely see is impossible transfer of mail to
> hotmail.com, yahoo.com and gmail.com servers.

We have a single, static IP and our DSL modem routes port-25 traffic to
a specific machine on our local network.  Local users pop-connect to
that machine to retrieve internet e-mail.  Some local users also use
that machine as the outgoing SMTP server, but others have changed their
outgoing server setting to that of our ISP - because some recieving
machines out there who do rDNS on our IP seem to object to the string
"PPP" that is part of the FQDN (we don't seem to have the ability to
change the rDNS given the type of service we are paying for).

I believe that our users are able to send e-mail to the above-mentioned
domains, and as I said above, any problems we have in ->sending<-
e-mail seem to stem from the rDNS of our static IP, and not because we
do not have an MX record set up for our domain.

> In my experience, though limited with non Windows installs, your mail
> server will have a performance issue in the end,
> trying to relay a message to these three domains but being unable to do so
> for the sole purpose that they don't recognize
> the reverse lookup or are unable to do one of your server/s.

The rDNS of our static IP is a function of our ISP.

Our MX record is not necessarily hosted by our ISP, but in any case is
under our total control, but (to my knowledge) is not involved in any
way with our server's ability to send e-mail or is not involved in how
(or whether) other servers receive e-mail from us.

> Having an MX and SPF record in place in the zone file will avoid any such
> issues.

Yes, I am looking into SPF records.  Where / who hosts the data?

> The alternative, since you seem happy not to receive spam, is to inform
> your mail server users not to send
> to the specified domains, however, it is nearly impossible to tell all your
> customers not to send from these domains.

I have verified that e-mail sent from Hotmail and Yahoo is reaching our
server.  I haven't tried G-mail but I believe that e-mail from G-mail
is also reaching our server.

> So way it carefully, the benefit of not getting spam, and the option of not
> getting potential customers emails at all.

Yes, that is the main concern (potential customers).

> If you keep it as is, also verify the functionality of your mail servers
> handling of retry when sending invalidated emails.
> You may end up stockpiling messages in the out que.

Our users get instant notification of failed send attempts.  As I noted
previously, some users have had to change the outgoing server to that
of our ISP because the rDNS of our static IP included the string "PPP"
(it was the presence of "PPP" that was mentioned in an error message of
a failed send attempt.  It was better back when we had no rDNS at all!)



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