[Host Unreachable] Exchange 5.5 Internet mail service 5

[gp8]

Hi , 99% of mails leave the IMS OK but a few will just sit and when looking at the details it says [Host unreachable]. I have tried nslookup to the host and get a valid response, I have even managed to ping the host in some instances
I have tried different dns servers address's with no result.
I have set the dns cache on the exchange server to force a dns resolution every time it sends a mail.
Any Ideas anyone???

Ged

 

[kilfarsnar]

I went another round with M$ yesterday. We are now at the point where it seems that the mail servers are making the connection, but then dropping it. I have this is my SMTP log:

4/17/04 5:24:36 PM : <<< IO: |354 Send binary data
|
4/17/04 5:24:36 PM : <<< 354 Send binary data
4/17/04 5:24:36 PM : <<< IO: |250 Ok
|
4/17/04 5:24:36 PM : <<< 250 Ok
4/17/04 5:24:36 PM : >>> DATA

4/17/04 5:24:36 PM : <<< IO: |354 Send data. End with CRLF.CRLF
|
4/17/04 5:24:36 PM : <<< 354 Send data. End with CRLF.CRLF
4/17/04 5:25:52 PM : 499 No routing hosts are reachable for domain.de. Message subject: ""RE: agenda LS GP meeting on monday 26.4."". Rescheduling delivery for later.

This is an unedited (except for the domain name) clip from the SMTP log. It seems to be about to send, but then returns the 499 error. I got some diagnostic tools from M$; Netmon and RPC Ping. So I will have to wait until I have another stuck message and test the connectivity for RPC over various protocols and all that. Why do I get the feeling it will all come out normal...

 

[gp8]

Hello all,

good news. I set up an smtp relay out on a dmz and had my mx records changed to suit, guess what? It appears to have done the trick. I can certainly now send mail to the domains I previously could not. I can only put this down to the "_" that is in my mail servers hostname and hence in the dns "my_server.maildomain.com". I can only say it appears to have worked in my case and that it may be worth a try for any of you with a similar setup. If you do try this good luck, I'll keep an eye on the thread to see if anyone else has success and if there is a cure for those of you who don't happen to have the dreaded "_".

Good luck everyone.

 

[msdIT]

Hi GP8 (Well done)
I was about to email something on the MX records but haven't had a chance to read up on how it all works.

So any chance of a more detailed explaination on what I would need to do. How do I do this change. Is it a big one that could stuff things up or easy. Remember I am not a Guru on this and a little inexperienced when it comes to the MX records. My clients server has a "_" as well, so you may well be onto the solution.
Let me know and I can test it.

 

[kilfarsnar]

Congrats GP8! I am in Germany, meeting with my IT Director this week. Yesterday we had the idea to redirect all mail destined for our .de domain to the German email gateway (relay) instead of sending it directly to the Exchange server. So far, I have had no problems or failures. But it has only been one day, so I consider the jury still out. If I have no failures for a month, I will consider it fixed. But your experience is encouraging. We can couple this with the fact that I have never had a failure with mail going over my relay. So the relay may be a key ingredient, lame as that is. Why the hell should a mail server need a relay to send mail?!?

I am skeptical as to whether an underscore in the domain name is a factor, as I do not have one in either domain name. But if this is an Exchange bug, it is not out of the question. If this scenario does fix the problem, it will be a slight disappointment, as we have not really found the cause, only engineered a workaround. But I don't complain when my users don't! Enjoy your DVD burner. msdIT, if you would like more info on MX records, I will be happy to assist to the best of my ability.

 

[msdIT]

kilfarsnar

I still need somebody to give me a bit more info on the implementation.

If it's a "work around" then so be it. I believe I'll be happy.

Hope that made sense.

 

[MarkAskew]

Well just to cheer you up - you are not alone. My 5.5 has now started to refuse to send attachments with a 'host unreachable' description. Emails without attachments work fine, also simple text documents work. Add a Word document, Excel, etc and it just holds in the queue. This seems to have just happened on its own for now reason so after pulling my hair out, was intrigued by this thread. Has anyone had any joy other than the '_' issue??

 

[kilfarsnar]

msdIT,

Basically, you need to set up a mail relay (not an open relay, but one that will deliver mail only to a specific address; your Exchange server) in a DMZ so that it can be reached from the Internet. Then you must call your DNS hosting company (probably your ISP) and have them point the MX record to your DMZ host (probably your firewall). An MX record is just a specialized DNS record that points to email servers. This is just an overview.

 

[msdIT]

kilfarsnar,

If it's a "work around" then so be it. I believe I'll be happy. I did say that but also followed it with a very important point "A Solution is preferable to a work around"

 

[kilfarsnar]

MarkAskew,

Make sure you don't have a message size limit imposed. Text is generally tiny, but Word and Excel docs can get big. Also, consider installing a mail gateway/relay in a DMZ. It seems to have helped others here, including myself.

 

[MarkAskew]

Thanks kilfarsnar but have checked this. No limits at all are set. Bit of a bizarre setup here...... we dont have access to our DNS servers - a third party look after these for us. Also the IMC connects through a proxy server which is located with another company. Guess what though, half hour ago the queues cleared and services have resumed. This clearly points out that it is not with our Exchange server but with the DNS or Proxy server (both of which are denying altering anything, but have run extensive tests). We have not applied the above patches but was dubious about this from the previous posts. If I find out anything, I'll post here.

 

[kilfarsnar]

Good for you Mark! It does seem that your problem is different from the rest of ours. It could be the other servers or a load on your Exchange server.

 

[tcswan]

Ok, What gives here?.. I've received email notices of 3 updated postings in this thread yesterday evening, yet they all seem to be gone this morning.. one from MarkAskew, one from kilfarsnar, and one from msdIT. Not one of them are showing up. Has the moderator cut all 3 postings?

Moderator: Let us hear from you re: why all these postings seem to be getting cut lately.. Nobody in here is spamming or flaming or creating any other problems that I've seen. We're all trying to get resolution to the same issue. If you continue to take issue with our postings, at least let us know why..

Thank you..

Tony

 

[theabear]

I wonder if the problem could be related to a recent security patch that was installed. Any thoughts?

 

[gp8]

Hello All,

over a week gone by now and still no complaints. I agree the relay option is a workaround but as it appears to have done the trick I'm happy.

msdIT,

Sorry for the poor diagram!!

inside net---------Firewall---------Internet
|
|
|
|
|
DMZ with SMTP relay

some links on setting up the relay. The example from skybuilders I found particularily helpfull.

http://www.skybuilders.com/Users/Jesse/Docs/howToSMTP.html

http://support.microsoft.com/default.aspx?scid=kb;EN-US;310336

http://winnetmag.com/Articles/Print.cfm?ArticleID=19619

You will need to contact your ISP and have your mx records changed to reflect the new hostname myserver.nydomain.com instead of my_server.mydomain.com. The changes should propogate within 24 hours.

 

[tcswan]

GP8,
Thank you for that post. I'll look into trying to set up a relay in a DMZ, but the confusing part to me is that we just don't have anything w/ an underscore in it, but maybe it will still work.

I appreciate the diagram and links as well.

Thanks again for all your help..

 

[gp8]

tcswan
I know and as other before have mentioned we may have more than one actual problem here showing similar symptoms. Anyway I hope this works out for you.

GP8

 

[ernestochirinos]

Hi All.
I read all the thread. I have experienced the same problem days ago.

I got some news.. I ran de Eseutil.exe to make a maintenance over de DB.. and the problem seems to dissapear..
All is working fine now..

Hope this help..

 

[ewiley]

Hey, just to add one more thing, i had this EXACT problem.. Fortunately I have a Watchguard firewall, and it's SMTP proxy allows outbound masquerading (which hides the server's name, among other things).. So if you have a Watchguard, you're in luck and don't have to rename or use an external proxy server.

--Karl

 

[DanElHombre]

I just went through this headache too.

I found out that the domain I could not deliver mail to had me blacklisted by ip address.

Something else to look into if your having the same issue.

 

[eric95]

I had this Host Unreachable problem with an old Exchange 5.5 server a little while ago. If I tried to telnet a clients listed MX record, port 25, I connected no problem.

Exchange ALWAYS gave me 'Host Unreachable'... No reason for it at all.

This is what I did to fix the problem.

Open Exchange Administrator
Internet Mail Service
Connections Tab
Specify by E-Mail Domain
Add a domain you always get Host Unreachable with, and select Use DNS, hit OK.

Restart Exchange Internet Mail Service.

Yes, it's stupid, but it worked for me... Using DNS is the default in Exchange, but if I take this extra step and tell it to use DNS *AGAIN* everything works...

Try it and let me know if it worked for you. Remember to restart the service.