Host Unreachable error

[UTTech]

I am running Exchange 5.5 on NT 4.0. One of the users tried to send a message to a valid e-mail address and received a host unreachable message but will not receive that message until almost 3 days later. I am able to send a message to that e-mail address from a personal account. PLEASE HELP!!

 

[rzs0502]

Are you able to see the domain from the Exchange server with nslookup?

If nslookup cannot resolve the domain, the domain name and IP must be added to your DNS server.

This failure to resolve the domain name generates the same error you mentioned.

When you dial up with your personal account, your ISP's DNS is able to resolve the domain name (so you can use this to check the IP of the domain)

Hope it works

RS

 

[UTTech]

When I tracert their domain name, I am able trace them successfully. I am also able to receive messages to users in that domain. However, when they tracert to my domain, it will time out when it reaches my ISP.

This is the point it times out:
16 81 ms 50 ms 50 ms Serial1.YRK-ptp02-PHL.Serial1-7.magpage.com
[216
.155.56.18]
17 * * * Request timed out.

 

[UTTech]

I got two messages in the event viewer:

Event ID 3010 An attempt to connect to host whatever.com failed.

Event ID 3011 An attempt to connect to host xx.xx.xx.xx was refused.

I looked in the IMS queue and noticed many messages in the Outbound messages awaiting delivery. When I click on the messages, it says, "Host Unreachable".

The MX record is correct.

 

[nacixem]

I had a similar incident. It had to do with Reverse DNS lookup. My site was trying to send email to an outside company that had an Exchange 2000 server that had Reverse DNS lookup options enable. Because their server couldn't resolve the name - it would reject the mail. They were using it as an anti - spam tool. hopes this helps.

 

[UTTech]

So are you saying that if I enable Reverse DNS lookup on my server, that will resolve the problem?

 

[nacixem]

No that the server receiving the email had

1. Exchange 2000
2. Reverse DNS lookup option enable

which cause the NDR to be created since the Exchange 2000 server couldn't confirm where the email was coming from.

The best thing to do is to talk to the person who is the DNS admin for your site or to the ISP that may be hosting your DNS server.

I hope this points you in the right direction.

 

[UTTech]

I also tried to NSLookup my host name and it resolved it correctly. However, when i tried to NSLookup the ip address, it says ns1.magpage.com cannot find 216.155.40.100: Non-existent domain.

 

[UTTech]

MY ISP enabled Reverse DNS lookup but I am having the same problem.

 

[devastator]

So are you hosting your own domain? What type of Internet connection do you have? If you are not hosting your own domain (your ISP does) do you have your DNS configured correctly to forward to your ISP's DNS servers for resolution?


Dev

 

[UTTech]

MagPage is hosting our domain and we have DSL through them as well. In IMS, under Message Delivery, "Use Domain Name System (DNS)" is checked. Am I supposed to "Forward all messages to host"?

 

[devastator]

Your ISP needs to point their MX records to the IP of your Exchange Server. You can do this by either having a public IP on your Exchange server or by use of NAT through a firewall or router.

Then in your IMS you have to configure your Exchange server to receive mail for your domain under IMS, routing tab. (Reroute incoming option checked, put yourdomain.com and go into routing restrictions and check off Host and Clients that authenticate and host and clients with these IP's. You don't have to put any ip's in though)

Also make sure your DNS service is setup correctly for IP to name translation. You can also configure a reverse lookup zone in your DNS as well. You can run a local DNS server for your internal network and have it setup with forwarders to point to your ISP's DNS servers for outside (Internet and Email Domains) resolution.

You may want to talk with your ISP about these options and see what they have to say since your connection is DSL with hardware and setting that I am not familiar with.


Dev

 

[UTTech]

Do I need a local DNS server?

 

[devastator]

I would highly recommend it for an internal network. If you are using this for home use or only have the one server then you could just use your ISP's dns.

 

[UTTech]

One thing I forgot to mention is that Magpage, my ISP, cannot send messages to that domain either. They say that the MX record is correct and Reverse DNS lookup is enabled on their DNS server. They can ping and tracert successfully.

 

[UTTech]

I also tried to nslookup

http://www.xxxxxxx.com

and was able to resolve to its ip address. If I nslookup xx.xxx.xx.xx, it says this:

ns1.magpage.com can't find xx.xxx.xx.xx: non-existent domain.

I tried several other domains and have no problems resolving both ways.