I have an Exchange 2007 mailbox that I migrated to Exchange 2013 and works fine. I migrated it back to Exchange 2007 and still works fine during coexistence with Exchange 2013. I try to migrate the mailbox back to Exchange 2013 and now it won't open in Outlook 2007. It says disconnected when it's trying to connect.  I can't figure out what's causing this.

Just try to access the mailbox using OWA first and check if thats working fine, do you have outlook 2013 by any chance try to check in the same if you are still facing the issue.

Also try to re-configure the profile in outlook 2007 and try.

Use this test analyzer provided by Microsoft to check the connectivity which you wants https://testconnectivity.microsoft.com/

For further info have a look on this blog post also:  http://blogs.technet.com/b/exchange/archive/2013/01/25/exchange-2013-client-access-server-role.aspx

However, if you wish you may also try some automation tools to get this job done more easily. One I can suggest you http://www.lepide.com/exchangemigrator/ which lets you to migrate and undo your migration with mail tagging facility to avoid duplicacy and other complications.

OWA works.  Tried deleting profile in Outlook 2007 and starting a new one and that didn't fix the problem. 

testconnectivity didn't find any problem.  All the mailbox that was migrated once are working without a problem.  Only mailbox that we're moved back to Exchange 2007 then migrated back to Exchange 2013 that are showing this problem with Outlook.

It works on Outlook 2011 for Mac btw. 

you may wanna try Outlook 2010 or 2013 then

do you have outlook anywhere enabled in Exchange 2007?

yes.  everything is working on all other mailbox in coexistence scenario except for mailboxes that were moved back to EX2007 then back to EX2013 again.  it will still work in OWA but not in Outlook 2007.

delete all profiles and create a new one. see if that works.

did you also check the connection status of outlook? It will show how it is connecting to exchange and which exchange server.

Hi,

According to your description, I understand that all mail client works fine after migrate mailbox form Exchange 2007 to Exchange 2013, however Outlook 2007 cannot connect to Exchange server when mailbox moved to Exchange 2007 then move back to Exchange 2013
If I misunderstand your concern, please do not hesitate to let me know.

Basis on previous steps testing, the mailbox  and mailbox database is available in Exchange server. How about another computer with same Outlook version and problematic account?
If it works in another client, please open Control Panel\User Accounts\Credential Manager in problematic computer, then clear the remains credential and try again.

This issue may be related to the connection between Outlook and Exchange server, please click Send/Receive All Folders or Update Folder to update data. Also, run Test E-mail AutoConfiguration and Outlook Connection Status with problematic account to narrow down issue. Please post relevant error message, its more helpful for further troubleshooting.

Thanks