Secondary smtp mail failure

Recently I've noticed that when I send an e-mail to a secondary smtp email address it is bounced back to me with an NDR saying that the recipient is not found, when it is clearly availiable.The primary smtp email address still works fine. Any ideas ?
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You need to do some testing. Both internal and external to Exchange.

Using the Exchange Admin tool, acquire the secondary SMTP address for the user. Using Outlook, manually type in that address; Exchange should auto-resolve it to the entry already in the directory; by default. This is normal. If this happens, there is no need to send the test message.

From an external ISP, send to the secondary SMTP address. What is the undeliverable message say? What does any undeliverable message say? Please obtain original undeliverable message & check headers if necessary to ensure proper routing was used. Should the message take the proper path and fail at the Internet mail connector, you will need to perform the steps I mentioned previously.

If more than one person administers the system, there is no guarantee something didn't change. A lot of times, an Administrator can change something without knowing the effects, or even applying a service pack or fix may do the trick. In any case, you may want to perform the steps I mentioned above. It can't hurt anything.

Does the secondary SMTP address use the same domain name as the primary?
bombheadAuthor Commented:
It certainly does ie. and the secondary is
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can you post the exact error message that you get?
Do you mean that you have both of SMTP addresses set for the same mailbox. What is the version of Exchange server?
Can you check if the issue remains if you set secondary SMTP address as a primary one?

You can configure multiple SMTP domain addresses on a single mailbox (i.e. and However, you must configure the internet mail connector to route e-mails sent to the secondary domain address internally to Exchange; else it will be returned as undeliverable because by default the connector only delivers e-mails bound for the primary domain address.

Under properties for the internet mail service, access the routig tab. Add an entry for and ensure it's routed inbound. Stop/restart the services.

External to Exchange, ensure e-mails destined for this secondary domain can make it to the Exchange internet mail service for delivery. Exchange is known for being robust & for the fact it can host multiple domains without incident.
bombheadAuthor Commented:
Everything was working a few weeks agao, in that the secondary domain would accept multiple addresses for a recipient, so I know that the config hasn't changed.FYI if I set the secondary mailbox as a primary then the mail fails, (Unknown recipient).
Can you check event log?
Turn on debugging.
What is the version of your exchange?
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