SMTP mail headers

This is a little odd. Could somebody please explain?

1) If I'm send a test message via my mail server and email client to a
hotmail account I get in the received header:

Received: from mail.mymailserver.com ([MY MAIL SERVER IP ADDRESS]) by
hotmailmailserver.com

2) If I do exactly the same thing (sending a message from the same
client and the only mail server in my organisation) but send it to
another web based mailbox (not hotmail) I get in the header:

Received: from UnknownHost ([MY MAIL SERVER IP ADDRESS]) by
thismailserver.com

***
So you would assume that that mail server isn't doing any DNS
resolution right? (UnknownHost).
***

3) If I send a test message from hotmail to the mail server that
previously came up with the UnknownHost address header (as stated in
step 2), this time it has in the header:

Received: from HotmailServer ([HOTMAIL SERVER IP ADDRESS]) by
thismailserver.com

I would expect it to say Received: from UnknownHost (?)

I'm confused about this behaviour, and it's consistant every time
Any ideas as to what may be going on?

Thanks

Alex

Re: SMTP mail headers

postings@alexshirley.com writes:

>1) If I'm send a test message via my mail server and email client to a
>hotmail account I get in the received header:

>Received: from mail.mymailserver.com ([MY MAIL SERVER IP ADDRESS]) by
>hotmailmailserver.com

Unfortunaly, mail servers do not always follow the standards. If
hotmail does follow the standards, then this indicates:

A DNS lookup of your IP address failed to return a hostname.
Therefore the parenthesized comment has only the IP address, but no
hostname.

Your system introduced itself with

HELO mail.mymailserver.com

and this fact is documented outside the parentheses. (It may have
use EHLO rather than HELO.

>2) If I do exactly the same thing (sending a message from the same
>client and the only mail server in my organisation) but send it to
>another web based mailbox (not hotmail) I get in the header:

>Received: from UnknownHost ([MY MAIL SERVER IP ADDRESS]) by
>thismailserver.com

This server is not following the standards. Instead of listing the
name from the HELO/EHLO command, it is listing the result of the
DNS lookup. Since the DNS lookup was not successful, it is
substituting "UnknownHost".

>***
>So you would assume that that mail server isn't doing any DNS
>resolution right? (UnknownHost).
>***

That was not my assumption. It looks to me as if it did a DNS
lookup, but it failed. A system that does not do DNS lookups is
likely to just list the IP address where the hostname belongs.

>3) If I send a test message from hotmail to the mail server that
>previously came up with the UnknownHost address header (as stated in
>step 2), this time it has in the header:

>Received: from HotmailServer ([HOTMAIL SERVER IP ADDRESS]) by
>thismailserver.com

That's consistent with my diagnosis above.

>I would expect it to say Received: from UnknownHost (?)

>I'm confused about this behaviour, and it's consistant every time
>Any ideas as to what may be going on?

I hope my explanation clarifies this.

Re: SMTP mail headers

Maybe I haven't explained this correctly (sorry)...

But from what I see (forgive me if I am wrong):

Sending a message from my mail server to hotmail worked correctly. In
the headers, the IP address and DNS lookup showed the name of the mail
server. All OK then!

Sending a message from my mail server to another web based mail account
didn't work correctly. In the header IP address there was no DNS name
resolution. So one MAY conclude that the other web based mail account's
server didn't do the DNS lookup correctly.

BUT Sending a message from hotmail to the other web based mail worked
correctly. IP address and resolved DNS name was there.

In a nutshell it appears (in the context of DNS name):

* The other web based mailserver resolves mails from hotmail fine.
* The other web based mailserver DOES NOT resolve mails from me.
AND YET
The hotmail server resolves mails from me fine!

Still confused.

Sorry (and thanks!)

Alex

Neil W Rickert wrote:
> postings@alexshirley.com writes:
>
> >1) If I'm send a test message via my mail server and email client to
a
> >hotmail account I get in the received header:
>
> >Received: from mail.mymailserver.com ([MY MAIL SERVER IP ADDRESS])
by
> >hotmailmailserver.com
>
> Unfortunaly, mail servers do not always follow the standards. If
> hotmail does follow the standards, then this indicates:
>
> A DNS lookup of your IP address failed to return a hostname.
> Therefore the parenthesized comment has only the IP address, but no
> hostname.
>
> Your system introduced itself with
>
> HELO mail.mymailserver.com
>
> and this fact is documented outside the parentheses. (It may have
> use EHLO rather than HELO.
>
> >2) If I do exactly the same thing (sending a message from the same
> >client and the only mail server in my organisation) but send it to
> >another web based mailbox (not hotmail) I get in the header:
>
> >Received: from UnknownHost ([MY MAIL SERVER IP ADDRESS]) by
> >thismailserver.com
>
> This server is not following the standards. Instead of listing the
> name from the HELO/EHLO command, it is listing the result of the
> DNS lookup. Since the DNS lookup was not successful, it is
> substituting "UnknownHost".
>
> >***
> >So you would assume that that mail server isn't doing any DNS
> >resolution right? (UnknownHost).
> >***
>
> That was not my assumption. It looks to me as if it did a DNS
> lookup, but it failed. A system that does not do DNS lookups is
> likely to just list the IP address where the hostname belongs.
>
> >3) If I send a test message from hotmail to the mail server that
> >previously came up with the UnknownHost address header (as stated in
> >step 2), this time it has in the header:
>
> >Received: from HotmailServer ([HOTMAIL SERVER IP ADDRESS]) by
> >thismailserver.com
>
> That's consistent with my diagnosis above.
>
> >I would expect it to say Received: from UnknownHost (?)
>
> >I'm confused about this behaviour, and it's consistant every time
> >Any ideas as to what may be going on?
>
> I hope my explanation clarifies this.

Re: SMTP mail headers

>In a nutshell it appears (in the context of DNS name):
>
>* The other web based mailserver resolves mails from hotmail fine.
>* The other web based mailserver DOES NOT resolve mails from me.
>AND YET
>The hotmail server resolves mails from me fine!
>
>Still confused.

Alex

Most SMTP servers do not do and reverse DNS resolution in order to
write the Recived header line. (Doing a RDNS lookup to eventually
block the message if no RDNS entry is present is another IMHO sad
story). They simply add what you told them with your "HELO/EHLO"
ommand. This DOES make sense since the IP is known at this time
anyways (from the TCP connection) and an interested party could later
on do an RDNS query of that IP any times. Replacing the HELO/EHLO
information with the result of an RDNS query seems a bad idea IMHO
cause valuable information is lost.

Anyways, the hotmail host seems to simply add what you have sent it
with the HELO or EHLO command whereas the other service you mentioned
aparently is doing an RDNS qurey which in your case seems not to give
a meaningfull reply.

HTH

Markus