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From: Simon on 4 Mar 2010 21:33
I have some questions on rDNS.

Q1.
Which domain will Sendmail use to check against the receiving IP
address for reverse DNS lookup? The domain in sender's address or the
envelop from address?

Q2.
If there is a reply-to header within the message, which domain will it
use for reverse DNS lookup? Still the sender's domain or the reply-to
header's domain?

Q3.
What will Sendmail do if it fails to match the reverse DNS? will it
drop the message silently or sending a bounce back message to sender
to notify on rejecting the message?

And if a bounce back message is sent, which address will it be
sending? The sender's address, the envelop from address, or the reply-
to address?


Many thanks.
Simon

From: D. Stussy on 5 Mar 2010 02:46
"Simon" <simon1212(a)gmail.com> wrote in message
news:b4793bee-359a-4ee6-a476-15b751d3924e(a)c37g2000prb.googlegroups.com...
> I have some questions on rDNS.
>
> Q1.
> Which domain will Sendmail use to check against the receiving IP
> address for reverse DNS lookup? The domain in sender's address or the
> envelop from address?

Neither. It takes the IP address and fetches the PTR record(s). Then, it
takes each label and fetches the address records (A or AAAA). If it finds
a match to the IP address it started with, that's a pass.

> Q2.
> If there is a reply-to header within the message, which domain will it
> use for reverse DNS lookup? Still the sender's domain or the reply-to
> header's domain?

Doesn't make a difference.

> Q3.
> What will Sendmail do if it fails to match the reverse DNS? will it
> drop the message silently or sending a bounce back message to sender
> to notify on rejecting the message?

Whatever you told it to do. It may drop or reject. Only idiots run the
check after message acceptance.

> And if a bounce back message is sent, which address will it be
> sending? The sender's address, the envelop from address, or the reply-
> to address?


From: Simon on 5 Mar 2010 04:29
On Mar 5, 3:46 pm, "D. Stussy" <spam+newsgro...(a)bde-arc.ampr.org>
wrote:
> "Simon" <simon1...(a)gmail.com> wrote in message
>
> news:b4793bee-359a-4ee6-a476-15b751d3924e(a)c37g2000prb.googlegroups.com...
>
> > I have some questions on rDNS.
>
> > Q1.
> > Which domain will Sendmail use to check against the receiving IP
> > address for reverse DNS lookup? The domain in sender's address or the
> > envelop from address?
>
> Neither.  It takes the IP address and fetches the PTR record(s).  Then, it
> takes each label and fetches the address records (A or AAAA).  If it finds
> a match to the IP address it started with, that's a pass.
>
> > Q2.
> > If there is a reply-to header within the message, which domain will it
> > use for reverse DNS lookup? Still the sender's domain or the reply-to
> > header's domain?
>
> Doesn't make a difference.
>
> > Q3.
> > What will Sendmail do if it fails to match the reverse DNS? will it
> > drop the message silently or sending a bounce back message to sender
> > to notify on rejecting the message?
>
> Whatever you told it to do.  It may drop or reject.  Only idiots run the
> check after message acceptance.
>
>
>
> > And if a bounce back message is sent, which address will it be
> > sending? The sender's address, the envelop from address, or the reply-
> > to address?- Hide quoted text -
>
> - Show quoted text -

Stussy,

Many thanks for your reply. Regarding Q1,

- Does it means Sendmail using the "relay" IP address to fetch the PTR
record?
- If the sender's mail server does not set up the PTR record, will the
checking failed even if it is a legitimate email (not a spam)?
- What do you mean by "each label"?
- Do you mean Sendmail will look for all domains to get the address
record (A) and compare with the "relay" IP ?

Simon
From: D. Stussy on 5 Mar 2010 14:46
"Simon" <simon1212(a)gmail.com> wrote in message
news:ddd8b31f-a756-4121-ba19-cc0b9bab3ae0(a)o16g2000prh.googlegroups.com...
On Mar 5, 3:46 pm, "D. Stussy" <spam+newsgro...(a)bde-arc.ampr.org>
wrote:
> "Simon" <simon1...(a)gmail.com> wrote in message
>
> news:b4793bee-359a-4ee6-a476-15b751d3924e(a)c37g2000prb.googlegroups.com...
>
> > I have some questions on rDNS.
>
> > Q1.
> > Which domain will Sendmail use to check against the receiving IP
> > address for reverse DNS lookup? The domain in sender's address or the
> > envelop from address?
>
> Neither. It takes the IP address and fetches the PTR record(s). Then, it
> takes each label and fetches the address records (A or AAAA). If it finds
> a match to the IP address it started with, that's a pass.
>
> > Q2.
> > If there is a reply-to header within the message, which domain will it
> > use for reverse DNS lookup? Still the sender's domain or the reply-to
> > header's domain?
>
> Doesn't make a difference.
>
> > Q3.
> > What will Sendmail do if it fails to match the reverse DNS? will it
> > drop the message silently or sending a bounce back message to sender
> > to notify on rejecting the message?
>
> Whatever you told it to do. It may drop or reject. Only idiots run the
> check after message acceptance.
>
>
>
> > And if a bounce back message is sent, which address will it be
> > sending? The sender's address, the envelop from address, or the reply-
> > to address?- Hide quoted text -
>
> - Show quoted text -

Stussy,

Many thanks for your reply. Regarding Q1,

- Does it means Sendmail using the "relay" IP address to fetch the PTR
record?
- If the sender's mail server does not set up the PTR record, will the
checking failed even if it is a legitimate email (not a spam)?
- What do you mean by "each label"?
- Do you mean Sendmail will look for all domains to get the address
record (A) and compare with the "relay" IP ?

Simon

-----------
IUf you expect further ansers from me, don't insult me by calling me by my
surname without a "Mr." prefixing it.


From: Bruce Esquibel on 5 Mar 2010 18:38
D. Stussy <spam+newsgroups(a)bde-arc.ampr.org> wrote:

> IUf you expect further ansers from me, don't insult me by calling me by my
> surname without a "Mr." prefixing it.


He probably should just refer to you as The Idiot.

Ever consider he's from a country that put their sirname first?

He probably thinks your first name is Stussy.

If you don't know the answer to his questions, just say so.

sheeese.

-bruce
bje(a)ripco.com
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