For the time being to get the account to work in Outlook you need to change the primary alias to a Microsoft domain account, such as @or @.
The Outlook Team is doing work that will enable some supported use of aliases in the near future.
STATUS: WORKAROUND Use Microsoft Edge or another web browser.
ISSUE The status of some connected accounts shows as “Update in progress error”.
Until then, you can change your From address to be the same as your primary Microsoft account alias.
For more information, read how to fix sends email "on behalf of" my email address.
Emails sent via on the web works correctly and emails will be sent with the correct email address.
NOTE: specify anything less than 5 minutes as very frequent checking could cause problems with Outlook and your mail server. Click Close then click OK to get back to your mail. In Outlook 2013, click on the Send/Receive tab at the top of the window. Click on Update Folder to force your Outlook check for new messages immediately. When the update finishes, click on the Home tab to get back to your Mail view 1.Last updated: May 21, 2018 Last updated: July 2, 2018 ISSUE Customers are currently unable to access Outlook.com/One Drive account pages using Internet Explorer, with the error "Upgrade your browser".Windows 10 users are unable to progress with any upgrade because Windows 10 includes the latest version of Internet Explorer. If you're using Outlook for Windows, see Fixes or workarounds for recent issues in Outlook for Windows.If you're having problems accessing Outlook.com, you can see the status of Microsoft Office Online Services at the Service Health portal.