Re: SBS 2003 - Exchange SMTP - send mail by DNS
From: Javier Gomez [SBS MVP] (javier_gomez_at_remove.this.engineer.com)
Date: 03/10/05
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Date: Thu, 10 Mar 2005 00:18:58 -0500
Hi David,
Definitely agree that DNS is more desirable (just like you I try to minimize
ISP "interference"). Using a smarthost is very "ISP dependent"... crappy
ISP, crappy smarthost. In any event I would like to point something out to
you...
> We were happy using DNS to send directly out from our Server [as it kept
> us in control and removed an external factor in terms of our ISPs mail
> servers] but as more and more ISPs and/or recipients use either automated
> blacklists that bounce dynamic IP addresses [even those that are in effect
> static such as ours] and/or reverse DNS checking [that would resolve to
> our ISP instead of to us - because we run POP3 mail...], we're being
> forced into one of 2 set-ups:
Reverse DNS doesn't work this way... what I mean is that using the POP3
connector has no effect on it. When you send mail using DNS the recipient's
mailserver will match the PTR record of your IP address with either a) the
EHLO greeting of the Exchnage (very common) or b) The sender's address
domain (extremely uncommon). As you can see, the fact that you are using the
POP3 connector (i.e. your ISP is hosting your mail) doesn't come into play.
So, if you have a static IP and you ask your ISP (the one providing you
internet service, not necessarily the same one as the POP3 mailboxes) to put
whatever.domain.com as the PTR record you should be fine.
> 1] Use Smarthost for ALL our outgoing mail, which means that any problems
> at our ISP become our problem in terms of sending mail outwards...
Yep.
> 2] Change from POP3 mail to SMTP mail and have our DNS set-up to resolve
> to our own Server on [our soon-to-be static IP address - once we change
> from cable modem to ADSL shortly...]. Then send all mail out via DNS.
As I mentioned earlier... you don't need to switch to SMTP. However, either
with POP3 or SMTP you still need to create those PTR records (if you want to
use DNS).
> That's kinda what I meant by the circumstances dictating what path we are
> having to take. Not a major gripe as such as I've always intended shifting
> us over to SMTP in any case but would have preferred it to be on our terms
> and timescale rather than it being necessitated by external factors.
Agreed. I'm a strong advocate of using SMTP, but I understand that POP3 is
easier, more manageable and somewhat more fault tolerant. You shouldn't be
forced to change something that you like.
> But yes, in relation to the original posting - simply using a Smarthost
> for all outgoing mail would be simplest.
Ok, ok... I know I went off topic on this one. I apologize! :-)
-- Javier [SBS MVP] www.msmvps.com/javier << SBS ROCKS !!! >>
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