5.5 MTA routing (Full Version)

All Forums >> [Microsoft Exchange 5.5] >> General


ponderMuse -> 5.5 MTA routing (30.Mar.2011 5:20:47 AM)


We have two Exch 5.5 servers in two different domains. We need to route emails from one domain to the other via external MTAs (outside exchange). We know the MTA connections are working fine. The problem we are having is that from one domain we can send emails to the other domain; but not the other way round. At the other end, from Outlook, when we send an email to a user on the other domain, we get undeliverable responses of the type: 'The recipient name is not recognized'.

A few things:
- We have not got an IMS connector setup in either Exch 5.5. (is this needed if all we want to do is route all outside emails via MTA connector?)
- We did at one point setup Directory Replication connectors but do we need these if all we want to do is route all outside domain emails via MTA connector?

Any help in understanding these matters are much appreciated.


lowthercat -> RE: 5.5 MTA routing (30.Mar.2011 5:55:01 AM)

Hi there and welcome!

This looks as though it's an MX resolution problem. The NDR messages that you are recieving are sent from the destination mail server, stating that it has checked the recipient access table (RAT) and found that no mailbox exists for that user. (Much like when you mis-spell an e-mail address).

Have you tried doing MX lookups for your destination domain? Can your MTA connection server correctly resolve the destination domain?

Let me know,


ponderMuse -> RE: 5.5 MTA routing (30.Mar.2011 7:01:18 AM)

Hello LowtherCat,

Thanks for the quick reply. I am not familiar with MX resolution issues. Is this something I can check by doing an nslookup on the delivery domain? If so, then I can't say for sure whether dns is set correctly (I'll check with the network administrator).

The scenario we have is that the source Exch server needs to route any emails to outside domain via an external MTA. The reason for this is that the email recipient's domain is not necessarily reachable.

For example, user@domainA.com sends email to user@domainB.com. Now, domainA is not able to reach domainB directly. Therefore, we simply want emails to domainB to be routed via an X.400 MTA we have set up where the MTA has @domainB.com specified in its address space list. Would we still need MX resolution on the recipient's domain in this case?


lowthercat -> RE: 5.5 MTA routing (30.Mar.2011 8:00:04 AM)

You have MSX 5.5 Enterprise Edition right?

There are different routing connectors that you can use.

1) PPTP Connector - Where a remote Exchange server dials into your LAN and collects mail at a specified period.

2) Site Connector - Mainly used for 2 sites that are in constant contact with each other, over MPLS.

3) X400 Connector - Mainly used for connected sites over Internet static IPSEC VPN tunnels.

4) Internet Connector - Routes mail externally via SMTP over the Internet.

If your domain B isn't directly connected to the Exchange server in domain A, then you need to be routing mail through a PPTP connector, (with domain B dialling into domain A to exchange messages) or an Internet Connector ( sending mail out through the Internet, either via an SMTP proxy or Direct DNS resolution).

I'm not sure where an X400 connector would come into play here?

ponderMuse -> RE: 5.5 MTA routing (30.Mar.2011 8:45:34 AM)

Yes, it is 5.5 Enterprise.

The routing we are trying to do was actually done previously (quite a few years ago). However, the documentation for the configuration of Exchange itself is not complete and the team working on it then have all left! We do know however that it definitely used X.400 connectors for routing. What's important to note here is that the Exchange servers in domainA and domainB do not connect to each other directly.

The idea is that a user in domainA sends an email to a user in domainB. In domainA, the Exchange 5.5 server sees that the message's recipient is @domainB.com. Therefore source Exchange 5.5 needs to route the message to a local X.400 connector (it has @domainB.com in its address list). This local X.400 connector is connected to another system also in domainA. This other system takes care of delivering the message to another similar system in domainB. Then, in domainB, the system connects to an X.400 connector local to domainB's Exchange server. Once in domainB's Exchange server, the message is delivered to the rightful recipient. See diagram below...

domA Exch 5.5 (x400)->(x400) domA legacy sys -> domB legacy sys (x400)->(x400) domB Exch 5.5

All we need is that in domainA, messages to recipients in domainB are routed via the local x400 MTA specified.

Thanks again for your help on this!


lowthercat -> RE: 5.5 MTA routing (30.Mar.2011 8:52:34 AM)


Last question I hope!
Do you use the other device in domain A to send all external mail, or just route mail to domain B?

ponderMuse -> RE: 5.5 MTA routing (30.Mar.2011 8:54:52 AM)

Ask away, no probs!

The other system should only receive and route messages destined to domainB.

lowthercat -> RE: 5.5 MTA routing (30.Mar.2011 9:09:50 AM)


I have a better idea as to just how you have this set up...

First thing:

How do you know that mail ISN'T being routed to your other forwarding system? When you send mail to domain B, which MTA queue do you see it pass through in the Exchange administrator?
Is it the queue for your X400 Connector?
If so, do you have logging / monitoring on your other system.. Do you then see the message arrive at the system and try to get delivered to domain B?

We need to find out at what stage the routing is going adrift. Exchange or forwarding system....

One thing I can say for sure... You messages are certainly hitting a mail server at the other end, (that's sending the NDR's back to you!) In that NDR, it should tell you the remote mail server name, is it the correct one for domain B?

ponderMuse -> RE: 5.5 MTA routing (30.Mar.2011 9:51:47 AM)

Currently, the messages are only getting as far as the local domain's Exchange server. I've turned on MTA logging in domainA's Exchange and I get the following warning each time I try to send a message to a recipient in domainB:

The MTA was unable to route to recipient C=US;A= ;P=MAIL;O=DOMAINA;DDA:SMTP=user1(a)domainb.com;. The message (MTS-ID): C=US;A= ;P=MAIL;L=X400SERVA-110330131426Z-296, recipient: C=US; A= ;P=MAIL; O=DOMAINA;DDA:SMTP=user1(a)domainb.com;, recipient number 1. Check the routing table for a possible incorrect routing configuration. [MTA DISP:ROUTER 12 119](12)

Now, the only place where I can see any sort of routing table is when I click on 'Site Addressing' section in Exch. In there I can see that domainb.com is associated with the X400 MTA connector to which we want to route @domainb.com messages. I've already recalculated the routing table and have also already restarted the MTA service just in case.

lowthercat -> RE: 5.5 MTA routing (30.Mar.2011 10:36:20 AM)

Alright... Good troubleshootng!

This really sounds like you have an MTA routing loop going on.

Have you recently added a new recipient to domain A? or possibly changed an e-mail address?

Exchange 5.5 doesn't share X400 namespaces by default, so if you add a recipient in domain A with an X400 address of domain B by accident, you'll make the routing fall down....

There is a workaround though.

Take a look here and you'll see what I mean...


ponderMuse -> RE: 5.5 MTA routing (30.Mar.2011 12:38:47 PM)

The link you mention lists the same three types of log messages we are getting. I am having a bit of trouble understanding exactly what the issue here is but I will have a closer look at it tomorrow and see what I can deduce from it all.

I'll let you know tomorrow how it goes!

Thanks once again,

ponderMuse -> RE: 5.5 MTA routing (31.Mar.2011 6:28:45 AM)


Taking a closer look at the Exchange logs, I am now seeing that the logs are mostly the same as the ones suggested in the mentioned link but with one difference; in my Exchange logs I am seeing this log entry:

Event ID 2256 - No attributes matching the string DN /O=MAIL/OU=DOMAINA/CN=CONFIGURATION/CN=SITE-MTA-CONFIG could be found in the directory.

Here I notice that the O/R is different to the one I've specified in 'Site Addressing' for X.400. I had specified it as C=US;A= ;P=MAIL;O=DOMAINA. (I edited the O/R address of the site after it was created)

Could it be that there is a discrepancy here? I am guessing that /O=MAIL/OU=DOMAINA was domainA's site O/R before I edited it in site addressing and changed it to P=MAIL;O=DOMAINA?

Page: [1]