Exchange and the default gateway

[TinRam]

Hello...


We are switching ISPs. Finally dumping the old 128K ISDN and getting a T1. The T1 is in and is all set up on a new router. However, our domain is still mapped to the ISP where our ISDN connection is coming from.

What I thought I could do is change the default gateway on the exchange server to point to the T1 router. This way the outgoing mail will go through the T1 and the incoming mail will still go from the old one. That way when we make the request to change the domain to the new ISP they can do it at their leisure and we don’t have to worry about it.

I was wrong.

When I change the gateway to the new router incoming mail (from the internet) stops coming in.

Exchange needs a default gateway for incoming internet mail?

Any comments?

 

[ashleym]

Ok heres how it works. You have a domain, for your domain you have an MX record for your mail server, which is mapped to a DNS name which resolves to an IP address. I am assuming that you are getting new real world IP's from the ISP that you are getting the T1 from. I am also assuming that these IP's are different from the ones you are using with your ISDN. You need to make a change in your DNS (where ever your domain is being hosted) and change the entry for your MX record so that it points to one of the new IP's (with your T1).

For email to reach your exchange server, it needs to know the identity of the mail server for your domain. For traffic to get from your LAN to the internet, there has to be a default gateway. They are not quite the same thing, but there are similarities.

Here's an example:

abc.com =123.123.123.1
MX 10 =123.123.123.2

DNS 1 =blah blah
DNS 2 =blah blah

So for the DNS info for your domain, you have a real world address (from ISDN ISP) for your mail server. Since your ISDN is going away and you have new IP's from your new ISP, change the MX record to reflect whichever new IP you want to assign to your mail serve.

Make sense? Hope so.

Ashley

 

[TinRam]

Thanks for your reply. As for the ISP stuff I am clear.

My question is only about the default gateway on the exchange server.

With the default gateway pointing to the new router and the domain mapped to the old router mail will not come in from the internet.

 

[ashleym]

The default gateway on the exchange server will only affect outbound traffic, inbound traffic is handled by DNS. Have you confirmed (using firewall logs) if smtp traffic is getting to your mail server? Is there anything in the event logs of the exchange server to suggest mail is not being accepted? Sounds like you may have internal DNS or networking issues. Have you tried to telnet to your mail server from home or somewhere outside your network? Does it work, probably not, try to telnet by DNS name and IP.

Hope this is more to your question.

Ashley

 

[GaryL]

TinRam,

AshleyM's definitely got you on the right track. It sounds like DNS issues.

Try these tests.
From an outside IP, telnet to the public IP mapped to your Exchange server on port 25, i.e. telnet 1.2.3.4:25
You should see something like
220 mailserver.yourdomain.com Microsoft ESMTP MAIL Service, Version: 5.0.2195.2966 ready at Mon, 12 Nov 2001 21:58:30 -0600
If not, the outside world can't talk SMTP to your Exchange Server. Check NAT mappings, port 25 access, etc. on your firewall.

Test to bypass DNS issues
Create a temporary Internet mail address in Exchange Admin on your mailbox using your public IP address of your Exchange server, rather than the domain name, i.e tinram@1.2.3.4. Set it as primary address temporarily.
Send a test email to a remote account. Reply to it from that account.

I've seen some ISP's are bad about not changing their DNS records--one took 2 weeks because their cache servers weren't being updated. You should check DNS info on a couple of DNS servers through NSLOOKUP.