Re: Blacklists and relays

Many thanks Bharat for your prompt response.

Jeff

"Bharat Suneja [MVP]" wrote:

Responses inline.

--
Bharat Suneja
MVP - Exchange
www.zenprise.com
NEW blog location:
exchangepedia.com/blog
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"jeffuk123" <jeffuk123@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message
news:97118A99-120A-499D-8E5C-436DF4D87A79@xxxxxxxxxxxxxxxx
Hello to all,

I have around 3 questions I would really appreciate some advice on.
Apologies for this.

1) We have exchange 2003. Our ISP is blocking many emails. Some emails are
bouncing back saying that they are on a CBL blacklist.

I contacted our ISP who state “Ideally, all of the blacklist companies
would
prefer reverse DNS to be set up for your static IP address”

Forgive me for asking but how does this work and how does it prevent
emails
from being blocked. I am aware that it all relates to spam?

Some mail systems check the sending SMTP host's IP address for a PTR record
(a resource record in the reverse lookup zone that maps an IP address to a
hostname). Generally, you're OK if a PTR record exists - it doesn't
necessarily have to return the fqdn of your server (though it's certainly a
good practice to have it set up to return the correct fqdn.. ).



2) Why are some emails blocked and others not? And what part do the
blacklist companies play in conjunction with the ISP?

Depends on the destination mail system's administrators - if they choose to
block mail from IP addresses that do not have a PTR or not.


3) If we have an Exchange server, do emails still go through an ISP
mailserver?

Depends on how you're setup - check your SMTP Connector for address space
* - do you see a smarthost or is it using DNS lookups? If you don't have a
SMTP Connector for *, check SMTP virtual server properties.



4)How does setting up relay with the ISP, and setting up a smarthost on
the
Exchange server differ from the point raised in question 3. I gather that
if
a smarthost and relay is setup, email goes to the ISP mailserver and they
forward it on to the destination. But does this not happen anyway?

No, not if you don't have the ISP mail server setup as a smarthost. Note,
you're still using the ISP's network for connectivity, but mail is delivered
directly to the host that the destination domain's MX record points to. In
case of smarthosts, you're delivering everything that's nont local (or for
which you don't have a SMTP Connector setup) to the smarthost, which would
then lookup MX records and deliver. You're adding one extra hop (or possibly
more, depending on ISP's mail setup) along the way with smarthosts.


Many thanks to all who take the time to answer these questions.

Jeff


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