I am currently running an Exchange 2007 and Exchange 2013 coesistance. When i migrate a mailbox from Exchange 2007 to Exchange 2013 the mailbox user can no longer use Outlook 2010. They can use Outlook 2013 with no issues but Outlook 2010 will not connect. The "Test email autoconfiguration" is correct with no errors, I am at the current Outlook 2010 Service Pack/Patch (14.0.7106.5001). When i delete the user profile and try to add the account fresh, I get the correct server settings (mailboxGUID@server.com) but when it trys to log into the server, i get a constant password prompt. Here is my Get-OutlookAnywhere | fl *authentication* settings:

ExternalClientAuthenticationMethod : Basic
InternalClientAuthenticationMethod : Ntlm
IISAuthenticationMethods           : {Basic, Ntlm, Negotiate}

This is the ONLY issue that is preventing me from finishing my migration and decommissioning the old server. I still have quite a few Outlook 2010 users.

Thank you for your help!

Hi,

Before going further,I'd like to ask the following questions to help troubleshooting:

1.After migrating,are all the user cannot use outlook 2010 or just a few?

2.When you directly create a new mailbox on Exchange 2013,could it use outlook 2010?

Thanks.