![image[15]](https://virtuallyaware.files.wordpress.com/2017/08/image15.png "image[15]")
Recently when working with a domain migration I experienced and issue with Outlook autodiscover working incorrectly for accounts that have been migrated to the target domain. The newly migrated users were keeping their same email addresses and their mailboxes were still hosted on O365 and all the appropriate object identifiers and directory synchronization (different article to follow on how this was done), but Outlook clients were failing authentication since is was trying to use basic authentication. Using the PowerShell command in the Link below to modify the tenant setting in O365, Outlook 2016 clients work pretty much immediately and Outlook 2013 can work with a registry modification. (Outlook 2010 and Outlook 2007 can not use Modern Authentication)
Enable or disable modern authentication in Exchange Online
