Post migration auto-complete returns “mailbox not found” errors

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We are in the process of doing a staged migration of our Exchange 2007 to a service from Microsoft (Please don’t hate me, it wasn’t my decision) that would host our Exchange service. After the migration the user converts from mailbox user to mail user. The email address converts from username@company.com to username@company.onmicrosoft.com. This is supposed to be seamless and the old address would auto forward/sync to the new one. After a user gets migrated, if someone sends them and email internally the sender gets an email with the message “The recipient’s e-mail address was not found in the recipient’s e-mail system. Microsoft Exchange will not try to redeliver this message for you. Please check the e-mail address and try resending this message, or provide the following diagnostic text to your system administrator”. We are unable to determine why this is happening for internal messages only. Anyone sending to us from outside the domain can send fine. Any help would be appreciated.

Rick Allen

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If you are using Office 365 you can have Exchange online take over the @company.com domain for email. No need to change any email addresses. You just have to follow the migration rules and tools for Office 365.

Joe

--Joe

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Thank you Joe, but we are doing a staged migration. Not all mailboxes at once. Would this still be the answer?

Rick

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There are many articles to read in the results at office 365 staged migration exchange 2007. Without knowing what you’ve done already it is difficult to know what you need to do.

Joe

--Joe

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Try deleting autocomplete nicknames:

Why Do I Get The Error ‘The Recipient’s Email Address Was Not Found In The Recipient’s Email System’ When Sending A Message To A Valid Recipient?

Windows 11 Pro version 22H2 build 22621.1778 + Microsoft 365 + Edge

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Try deleting autocomplete nicknames:

Bruce, this was our thought. We set Group Policy to delete the nk2/auto-complete files from the local computer and then disable the feature until after the migration. Doing it one mailbox at a time would be too cumbersome with 300+ people to migrate.

We were hoping to find another way.

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I suspect you need to update AD for migrated users to add the MS address as the preferred email and keep the old. Mail should then be forwarded automatically. I assume you have a connector to send email to the MS domain?

I agree that using an MS domain name is not a good idea, but I can’t see how you can do otherwise with a staged migration. You should be able to change the email domain back post migration.

cheers, Paul

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I suspect you need to update AD for migrated users to add the MS address as the preferred email and keep the old. Mail should then be forwarded automatically. I assume you have a connector to send email to the MS domain?

Paul, yes we have a connector. Adding the other domain to our email addresses was shot down by our Director. His thought was that it would confuse the Exchange server and put it in an endless loop not knowing where to send the email. Thank you for the idea though. I guess what we are looking for is a way to force companyname.com to automatically find companyname.onmicrosoft.com. Your suggestion sounded like a good idea to me, but he didn’t like it.

Rick

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He might not like it but that’s how you do it. Why not try it for one test user?

cheers, Paul

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He might not like it but that’s how you do it. Why not try it for one test user?

Actually, I just looked at his account since his is the only one migrated completely so far. He does have the other account address as an alias and it doesn’t help for people using auto-complete. Some on domain can send to him, others are unable and there is no rhyme or reason for it. All users are set the same. My mailbox has been partially migrated. There is a step left that will finish the process. In the meantime I have to login to my web interface on Office365 to receive email and use my Outlook on my desktop to send email. Replying is very cumbersome! 😉

Any other thoughts on this would be appreciated.

Rick

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Moving the director first was very brave, hope it was his idea!

The “new” address should be the primary and the “old” the alias.
Check that the nicknames are not inserting X400 addresses – the old MS standard. If they are there is no work around and you have to delete the nicknames.

cheers, Paul

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Moving the director first was very brave, hope it was his idea!

Yes, it was his idea and he actually did it. He’s the only one so far the has been doing the migrations. Him and me.

The “new” address should be the primary and the “old” the alias.
Check that the nicknames are not inserting X400 addresses – the old MS standard. If they are there is no work around and you have to delete the nicknames.

We do have X400 addresses in our email address list, but they are left over from when we migrated from Exchange 2003 to Exchange 2007. They have not been an issue as yet. Can’t we just delete the X400 address? Do we have to delete the whole user profile?

On another note, he now can send an email and have the return address show username@companyname.com. That issue is fixed. However some, not all, people who send new email to him or me using the auto-complete feature in the “to” line get bounce backs. This was the original issue of this thread and it has not been resolved short of disabling the feature for all users via Group Policy. Why can’t the address in the auto-complete authenticate to the server when it’s the same address as the return address listed when we sent emails out?

Rick

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You need someone with a bounce to send you the raw email so you can see what address they have used.

X400 addresses are used up to Exchange 2010 – I think.

cheers, Paul

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