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Exchange 2000 Not Trying Next MX Record

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by viperian

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Hiya,

I have a big problem with a Exchange configuration. Server is a Windows 2000 server with SP4 and Exchange 2000 server with SP3 + SP3 Post september 2003. After applying these Service packs the trouble started. DNS correctly gets all mx records for email directed to the outside world.

Problem:

For a customer where i have to deliver email there are 3 mx records available, namely (fiction)

mail.customer.nl 10 mx preference (unreachable)
fallback.customer.nl 20 mx preference (unreachable)
relay1.isp.nl 100 mx preference
(active)

Exchange tries to deliver to the first 2 adresses and then stops. It doesnt deliver to the relay server.

I have the same problem with other adresses where the first is their own mailserver and second or third is a relay server with an provider.

If the first or second mx record is up there are no problems with mail delivery.

The problem is if their are more then 1 MX record and the 1 or second mx record

16 replies

by viperian

Seems like the last line died on submit. :(

I was trying to tell that if the servers pointed @ by the first or second MX record are unavailable the server doesnt deliver the email even if there is a third or fourth MX record pointing to a relay server which is Active and accepting email.

by cg it

your problem may not be with you but with the relay servers at the ISP. An active relaying mail server is virtually unheard of nowadays with the focus on spam prevention so before pulling your hair out and popping the vallum that the problem is yours, check with the ISP guys and see if they've done something on their end like no longer allowing relaying.

by viperian

I dont use a relay server i deliver the mail through DNS direct to the addressed party. I can also see that outgoing mail is only directed to the first mx record and sometimes the second mx record. These problems arose after installing SP4 for Win2K and SP3 for exchange 2000, before that the problems werent there.

by mjost

When this happens are there any Event log errors -ie Non-Delivery Reports Event ID 756 or Event ID 4000 messages logged in the Application Event log? Or is this mail sitting in the queue awaiting delivery?
Are you using a SMTP front-end servers?
ISP using dial-up connections?

by viperian

There arent any NDR reports or other event log messages, also i dont use a front-end server construction. Also not using dialup usingT1 as a connection straight to internet.
Exchange tries to deliver the message to the external recipient, but stops with the first or second mx record. If those two give errors like 10051 (netowrk unreachable) and timeout it waits for the next time it is triggered for delivery.

Momentairly i use a smtp gateway infront of the exchange servers (smart host), which solves the problem but if i switch back to letting exchange deliver the emails straight forward through dns to the internet it fails with some.
so solution must be found in exchange 2000, but still haven t found it yet :(

by mjost

ok, Turn on full debug reporting and test it again to see whats up with the outbound email.

Enabling Debugging Level Logging If you are experiencing mail flow issues and want to view all events, you can modify a registry key to set logging to the highest level (level 7).

To setup troubleshooting Mail Flow

To enable logging at the debugging level
1. Start Registry Editor: From the Start menu, click Run, and then type regedt32.
2. In Registry Editor, locate and click the following registry key: HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\ MSExchangeTransport\Diagnostics\SMTP Protocol
3. Set the value to 7.

by mjost

Also, assuming your DNS is correct, the outbound messages are routed to the connector or to the outbound SMTP virtual server that is responsible for delivery. Check for very simular Virtual Server names which cause issues I understand.

Is this on a DC? If so, instead of modifying the default SMTP virtual server, it is recommended that you either create an additional SMTP virtual server or create an SMTP connector to override the default virtual server settings. In many instances, it is preferable (but not required) to set up an SMTP connector to handle outbound mail.

To configure your SMTP virtual server to deliver outbound mail you must:
Ensure that the outbound port is set to port 25 (this is the default setting). Allow anonymous access for your outbound connection (this is the default setting). Set external DNS servers for SMTP to use, if desired. You can configure the SMTP virtual server to use an external DNS server; however, it is easier and more common to rely on your internal DNS servers to forward mail to trusted external DNS servers.

by slartibartfast

OK, The first thing you have to do is check whether your DNS server is able to resolve the smtp server referenced by the failing MX record (using nslookup from a DOS prompt on the *Exhange Server*.

If it can , then (also from the dos prompt) see if you can actually establis a session on Port 25 with the recipient server. A little-known but incredibly useful way of testing this is to use Telnet from the DOS prompt, so in your case 'Telnet relay1.isp.nl 25' (the 25 tells it to use the SMTP port). If the server is reachable, you'll see the DOS screen clear and the SMTP welcome prompt.

My guess is that you won't be able to reach the server this way. If you can't, then try it from another computer not on your network. If that can't either, it's probably the recipient server, not Exchange or DNS

Andrew.

by viperian

DNS is able to resolve the addresses tested with nslookup, also can telnet to port 25 from command prompt. This problem arose when W2K got up to SP4 and exchange 2000 got up to SP3. Also loaded all hotfixes suggested by Microsoft. I now use a workaround with a email virus scanning gateway which works fine.

by thiesi

We've got almost the same problem over here. It is not related to DNS or routing issues of our network, but to some problem with the Exchange server itself.

I can
- nslookup the backup MX servers in question
- ping the backup MX servers in question
- perform a "manual" (i.e. via telnet) SMTP session with the backup MX servers in question.

It seems like Exchange is ignoring all other than the first (i.e. the one with the lowest number) MX records. The messages keep sitting in the queue until their maximum hold time is reached.

The system is a W2K Server, running Exchange 2000 Enterprise (both German language versions) with all the latest Service Packs applied.

I'd appreciate any help.

Thanks in advance,
bye, K&K,
T-Zee

by eric

I think your problem is that you are using a terminal MX weight. MX weights of 1 are ALWAYS used regardless of their up/down status. MX weights of 100 are NEVER used regardless of if they are the only system up. Example:

MX 1 inbound1.mycompany.dom
MX 10 inbound10.mycompany.dom
MX 20 inbound20.mycompany.dom

In this example, SMTP will never connect to inbound10 or inbound20 even if inbound1 is down. This is because the MX weight of 1 says to always use it, period.

MX 10 inbound10.mycompany.dom
MX 20 inbound20.mycompany.dom
MX 100 inbound100.mycompany.dom

In this example, inbound100.mycompany.dom will never be used because the MX weight 100 says to never open a connection to it. This weight is used when you have a Spam Filter on another IP address than your outbound SMTP and the destination uses reverse DNS authentication. That way the target SMTP box can find your real SMTP host in DNS, but mail will never be sent directly to it.

Aloha,

Eric

by viperian

Sorry isnt the problem, because we tried alot of things including other email servers, which didnt have the problem so we know problem is situated in Exchange 2K in combination with W2K. But thanks for the info always good to see people help and think with ya.

grtx,
Edwin

by viperian

Isnt the solution, Microsoft has stated that it is a problem with SP4 on W2K and SP3 on Exchange 2K. This combination and using exchange 2K on a domain controller. I could choose between moving exchange 2K from the domain controller or move to exchange 2003. I used another solution because both werent an option. I use a Symantec SMTP 4.0 gateway so i can control spam and in - outgoing viruses. I put a smtp smart agent in all Exchange servers we use (3x) and it all works great now.

Inbound
Internet --- Firewall (accepts email) --- Symantec GW --- Exchange server (Bridge head server)

Outbound
Exchange server/Exchange server/Exchange server --- Symantec GW --- Firewall --- Internet

Thanks all for participating in this problem/challenge.

Grtx,
Edwin

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