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Sending email from Exchange 2003 server to pop account with same domain dame wont work.

bgagnon asked
Medium Priority
Last Modified: 2007-12-19

here  is my setup: I have a smtp server which is also the main MS record for domain xyz.net.  This gateway also has some pop3 account for the domain xyz.net. I have set the gateway to forward all mail to my Exchange server when the email does not exist on the pop server.

My problem is that since we upgraded to Exchange 2003 smtp work differently from exchange 5.5 IMC.

I did remove the check box this this exchange organisation is responsible for all mail delivery to this address on the xyz.net recipient policy.

I also can not add the gateway to forward all mails with unresolved recipients to host in mesages folder in Default SMTP Virtual server propreties because with all the mails that are sent to unexisting address from spammers I create a loop from Exchange to gateway.

I know I need to create two separate rule for incomming and outgoing from Exchange 2003 but I am not familiar with the routing of exchange 2000/2003.

Can you help?  Thanks
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We recently battled this problem on an exchange 2003 rollout (also from 5.5)..  Exchange 5.5's IMC used to deliver mails to the MX host (in your case your gateway) if the recipient was unknown. We took the same steps you did, we told Exchange2k3 that it was not responsible for all mail in the domain, and told it to forward all unresolved recipients to our mail hub.

It sounds to me like the mail hub is your problem. I don't know what MTA you're running, but we're using sendmail and had already used the aliases file to route mail for our users. If you did the same, it would fix your looping issue.

So your gateway has an aliases list and is told that it accepts mail for domain xyz.com. if your gateway was called gateway and your 2k3 box was called exchbox your aliases entries would look something like this:

# pop3 users whos accounts are on gateway
melvin: melvin@gateway
betty: betty@gateway
# exchange users
joemama: joemama@exchbox
mary: mary@exchbox

one minor glitch with this methord that (depending on your MTA) you may have to make an MX record for exchbox.domain.com pointing at itself
the bigger glitch is you have to add an email address to each exchange recipient, within exchange 2k3. (we've been doing things this way, even with 5.5 for many years so we're used to it - we have 7 sites and 7 exch servers..)
so user joemama would have to have a joemama@xyz.com email, and a joemama@exchbox.xyz.com address in exchange, otherwise mail WILL bounce.

If things are config'd this way, inbound mail will flow as it did before, outside -> sendmail (aliases) -> exchange mailbox
spammer mail to unknown recips will hit the gateway, and get NDRd and returned from there, never hitting the exchange box
mail from exchange users to pop3 users will get forwarded because you told the SMTP virtual adapter to send mails to "unknown" recipients to gateway
badabing all fixed.

if you're new to the aliases file dont forget you need to do a newaliases after every change. postfix and most other MTAs have similar functionality if you're not running sendmail on your gateway.
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and first thanks for your help.

All this was already considered but rejected for duplication reason.  We simply dont want to maintain 2 lists of emails.  Technicly it easy to and understand but in your opinion, is there any other way to get the job done?

Well - the problem is that you have to have some mail hub who is aware of where all mailboxes reside. If you don't want to keep two lists you could make the exchange server your mail hub, and first point where mail comes in from the net. You'll have to lock it down to prevent relaying, and keep it patched up to date 100% to prevent attacks, but it would allow you to just have one "list" and it would be your global address list..

We still have a lot more faith in unix for this sort of routing job, but we're biased and for now we don't mind editing an aliases file. :) I can totally see where you're coming from.

With this sort of a set up you would create the contacts (formerly custom recipients) like i mentioned before, pointing to the pop3 mailboxes on the other server. Tweak your firewalls, network layout (if necessary) and MX record so that your inbound mail now lands on your exchange server rather than on "gateway". I don't know what MTA you run on your pop3 server but you may need to tell it (if it's the pop3 people's SMTP server as well) to forward unknown recipients to the exchange server, if it isn't already.

So mail paths now will look like:
Inbound Internet mail to exchange recips will deliver at the exchange box, and inbound Internet mail to the pop3 people will be forwarded to your pop3 server.
Mail from exchange users to the pop3 users will fwd to the pop3 folk's via "contacts"/custom recipients
Mail from pop3 users to exchange users will fwd to the exchange box and get delivered there
Mail from exchange users to the net will go out the internet mail service directly
Mail from pop3 users to the net will go directly out from the pop3 server's MTA, or from the exchange box if you have those clients use it as their SMTP server instead of the pop3 server's MTA.

This should work fine and should allow you to keep one list.

In fact, I like the sound of this so much that I'm going to talk to my unix and exchange sysadmins next week about moving to this to simplify our aliases mess =D



Hi pfftdives,

Mail from exchange users to the pop3 users will fwd to the pop3 folk's via "contacts"/custom recipients.  How do you do that. Both users have the same @company.com email. You define a new domain for the pop3 and keep both adress in the contact?

My pop3 is a Merak server.  Could I solve the problem by replacing my pop 3 with an Exchange server and put only the pop3 users on it and open the port needed for exchange to work from the dmz to the inside network

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