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Old 04-10-2008, 02:54 AM
"Hugh E Cruickshank"
 
Default Force sendmail outbound routing for specific domain name

CentOS 4.6

Hi All:

Is it possible to force sendmail to use a specified host name for
outbound email to a selected domain name instead of the host name
that can be found by looking up the DNS entry?

The problem is that we have a client that uses the same ISP as we
do and the IP addresses assigned to both of us are very close. This
has resulted in connection problems specifically with our outbound
email to the client. I believe it is an issue with TCP/IP routing.
In the past the ISP has setup some sort of special routing that
redirects our email to the ISP's backup mail server which then
delivers the mail to the client. Every once in a while the ISP does
something with their configuration and the routing override is lost
for several days until we can get them to recognize the problem
and then figure out what they did the last time. This happened
over the weekend and we are still waiting on the ISP to fix it up.

My thought was can we configure this in our mail server so that we
and our client do not have to suffer with this again?

TIA

Regards, Hugh

--
Hugh E Cruickshank, Forward Software, www.forward-software.com
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Old 04-10-2008, 03:00 AM
Frank Cox
 
Default Force sendmail outbound routing for specific domain name

On Wed, 09 Apr 2008 19:54:28 -0700
Hugh E Cruickshank <hugh@forsoft.com> wrote:

> Is it possible to force sendmail to use a specified host name for
> outbound email to a selected domain name instead of the host name
> that can be found by looking up the DNS entry?

I'm not entirely sure that I understand your problem. If you have a unique
domain name, and your client also has a unique domain name, and your dns
records are properly configured, then sending email from domain name A to domain
name B should just work, regardless of how close your actual IP addresses are.

Having said that, you can put a domain name and IP address in /etc/hosts on the
originating computer and that computer will henceforth use the IP address
specified there.

--
MELVILLE THEATRE ~ Melville Sask ~ http://www.melvilletheatre.com
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Old 04-10-2008, 03:21 AM
"Hugh E Cruickshank"
 
Default Force sendmail outbound routing for specific domain name

From: Frank Cox Sent: April 9, 2008 20:01
>
> On Wed, 09 Apr 2008 19:54:28 -0700
> Hugh E Cruickshank <hugh@forsoft.com> wrote:
>
> > Is it possible to force sendmail to use a specified host name for
> > outbound email to a selected domain name instead of the host name
> > that can be found by looking up the DNS entry?
>
> I'm not entirely sure that I understand your problem. If you
> have a unique
> domain name, and your client also has a unique domain name, and
> your dns
> records are properly configured, then sending email from domain
> name A to domain
> name B should just work, regardless of how close your actual IP
> addresses are.

I agree whole heartedly that it "should just work" but time and time
again we have see where it does not work.

> Having said that, you can put a domain name and IP address in
> /etc/hosts on the
> originating computer and that computer will henceforth use the IP
> address
> specified there.

That would work if I was looking to use a specific IP address but
would like to use a specific host name. For example I would like
all mail outbound to example.com to bypass the DNS/MX entry of
mail.example.com and use instead backupmx.isp.com not just the IP
Address of backupmx.isp.com.

Thanks muchly for your suggestion.

Regards, Hugh

--
Hugh E Cruickshank, Forward Software, www.forward-software.com
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Old 04-10-2008, 03:32 AM
Clint Dilks
 
Default Force sendmail outbound routing for specific domain name

Hugh E Cruickshank wrote:

From: Frank Cox Sent: April 9, 2008 20:01


On Wed, 09 Apr 2008 19:54:28 -0700
Hugh E Cruickshank <hugh@forsoft.com> wrote:



Is it possible to force sendmail to use a specified host name for
outbound email to a selected domain name instead of the host name
that can be found by looking up the DNS entry?

I'm not entirely sure that I understand your problem. If you
have a unique

domain name, and your client also has a unique domain name, and
your dns
records are properly configured, then sending email from domain
name A to domain
name B should just work, regardless of how close your actual IP
addresses are.



I agree whole heartedly that it "should just work" but time and time
again we have see where it does not work.


Having said that, you can put a domain name and IP address in
/etc/hosts on the

originating computer and that computer will henceforth use the IP
address
specified there.



That would work if I was looking to use a specific IP address but
would like to use a specific host name. For example I would like
all mail outbound to example.com to bypass the DNS/MX entry of
mail.example.com and use instead backupmx.isp.com not just the IP
Address of backupmx.isp.com.

Thanks muchly for your suggestion.

Regards, Hugh


Hi, It has been some time since I have had to do anything with Sendmail
like this, but I believe mailertable is what you need. See
http://www.sendmail.org/m4/mailertables.html


Hope this helps

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Old 04-10-2008, 03:39 AM
"Hugh E Cruickshank"
 
Default Force sendmail outbound routing for specific domain name

From: lists-centos Sent: April 9, 2008 20:29
>
> you could use the sendmail "smarthost" setting to dump all your
> outbound mail on your isp's mail server.

We used to do that on our old SCO OSR5 box but I stopped doing that
when I switched over to the new CentOS4 system. For the life of me
I can not recall why but I must have had a reason. I will check that
out as an alternative.

> you don't explain what the problem is, e.g., inability to connect to
> their server, etc.

The connection to the client's mail server times out.

> of course the real solution is to resolve the underlying problem
> since of course the isp's kludge will break now and then.

Too true. Eventually we will be moving the whole shebang to a co-lo
facility so that will probably avoid the problem as well (a little
overkill but it should work).

Thanks, Hugh

--
Hugh E Cruickshank, Forward Software, www.forward-software.com
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Old 04-10-2008, 03:42 AM
"Hugh E Cruickshank"
 
Default Force sendmail outbound routing for specific domain name

From: Clint Dilks Sent: April 9, 2008 20:32
>
> Hi, It has been some time since I have had to do anything with
> Sendmail
> like this, but I believe mailertable is what you need. See
> http://www.sendmail.org/m4/mailertables.html

Give the man a cigar! That looks like precisely what I need.

> Hope this helps

I am sure it will.

Thanks muchly!

Regards, Hugh

--
Hugh E Cruickshank, Forward Software, www.forward-software.com
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Old 04-10-2008, 03:59 AM
"Hugh E Cruickshank"
 
Default Force sendmail outbound routing for specific domain name

From: Hugh E Cruickshank Sent: April 9, 2008 20:43
>
> From: Clint Dilks Sent: April 9, 2008 20:32
> >
> > Hi, It has been some time since I have had to do anything with
> > Sendmail
> > like this, but I believe mailertable is what you need. See
> > http://www.sendmail.org/m4/mailertables.html
>
> Give the man a cigar! That looks like precisely what I need.
>

Well that did seem to work. At least the email is being delivered
to the ISP's backup mail server now. I will not know until tomorrow
if the mail actually makes it through to the client but then that
an issue between the client and the ISP.

Thanks again.

Regards, Hugh

--
Hugh E Cruickshank, Forward Software, www.forward-software.com
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Old 04-10-2008, 04:09 AM
Les Mikesell
 
Default Force sendmail outbound routing for specific domain name

Hugh E Cruickshank wrote:

From: Clint Dilks Sent: April 9, 2008 20:32

Hi, It has been some time since I have had to do anything with
Sendmail
like this, but I believe mailertable is what you need. See
http://www.sendmail.org/m4/mailertables.html


Give the man a cigar! That looks like precisely what I need.



Note that you don't need to do the makemap stuff - that's already
include in the Centos setup. Just put the text suggested in the
mailertable file and restart sendmail. And if you use a literal IP
address, enclose it in []'s like it says for hostnames where you want to
avoid the MX record lookup.


--
Les Mikesell
lesmikesell@gmail.com
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Old 04-10-2008, 04:21 AM
"Hugh E Cruickshank"
 
Default Force sendmail outbound routing for specific domain name

From: Les Mikesell Sent: April 9, 2008 21:10
>
> Hugh E Cruickshank wrote:
> > From: Clint Dilks Sent: April 9, 2008 20:32
> >> Hi, It has been some time since I have had to do anything with
> >> Sendmail
> >> like this, but I believe mailertable is what you need. See
> >> http://www.sendmail.org/m4/mailertables.html
> >
> > Give the man a cigar! That looks like precisely what I need.
> >
>
> Note that you don't need to do the makemap stuff - that's already
> include in the Centos setup. Just put the text suggested in the
> mailertable file and restart sendmail. And if you use a literal IP
> address, enclose it in []'s like it says for hostnames where you
> want to
> avoid the MX record lookup.
>

All that was needed was to add the entry to /etc/mail/mailertable and
run "service sendmail restart". It rebuilds the database for you. I
did not worry about the IP Address or the MX but it seems to have
worked anyway.

Regards, Hugh

--
Hugh E Cruickshank, Forward Software, www.forward-software.com
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Old 04-10-2008, 12:08 PM
"Brent L. Bates"
 
Default Force sendmail outbound routing for specific domain name

Your problem sounds like it has nothing to do with sendmail, but with any
IP traffic. Does the other company have a Web or FTP site at the same IP
address or with in the same class C? If so, when email doesn't work, I bet
neither of these work either. I've seen this happen before. The ISP isn't
properly routing traffic between your two networks. I'm not sure you if you
could put in a static route that would by pass your ISP's faulty routing
tables or not. I'm betting probably not.

--

Brent L. Bates (UNIX Sys. Admin.)
M.S. 912 Phone757) 865-1400, x204
NASA Langley Research Center FAX757) 865-8177
Hampton, Virginia 23681-0001
Email: B.L.BATES@larc.nasa.gov http://www.vigyan.com/~blbates/

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