NEW Outlook app: how to add an IMAP account with user name different from email address?

I had the same issue. I was able to get round the issue of a different logon id to the email address by setting the account up in control panel -> mail settings and adding the account there where it allowed a different user name

I also had another issue - the set up now insists on sending a test mail successfully. Unfortunately the mail sever I was using requires a mail pick up before sending. Of course setup doesn't do this. I got round this issue by ensuring I was logged on via webmail first and then doing the mail set up.

This is really really annoying. All my family email addresses have different IMAP login user names from their actual email addresses - just how the hosting provider sets them up and now we cannot use Outlook as there is now way to actually add these types of accounts. How can Microsoft miss something as obvious as providing a user name box??

Is there any indication when this might be fixed?

Same here, almost a year later. And today they disabled the old Outlook, I can't switch to it anymore, just the new one. Still not fixed. This is the worst piece of garbage from MS since I remember. Switching to another email client.

This is really really annoying. All my family email addresses have different IMAP login user names from their actual email addresses - just how the hosting provider sets them up and now we cannot use Outlook as there is now way to actually add these types of accounts. How can Microsoft miss something as obvious as providing a user name box??

Is there any indication when this might be fixed?

Yes quite agree, unbelievable that they could write this new app without the functionality to set the user name ... and still haven't resolved it months later, April 2024.

It even messes up accounts imported from the old Mail app, which used to work fine. Even worse Microsoft now force you to the Outlook App when you try to run the old Mail app so now have to go looking for a different mail client.

The lack of IMAP settings options in the New Outlook causes duplicates of my e-mails in the SENT ITEMS folder. Normally, there should be an option for IMAP to uncheck "Save a Copy of Sent Messages on the Server". But, alas, this setting is nowhere to be found in this dumbed-down e-mail client.

Here too in April 2024. Until "The new Outlook" I was able to configure an IMAP username which is not the email address in ALL free Microsoft email client products since 1998. Now it seems Microsoft doesn't WANT users to use their free email software anymore, except you bought Office 365 or use Live (which is a Spam hell since a few years btw.).

After 6 months I don't expect that this is getting better (and since I need to read my email...), so I have no choice and change to Thunderbird. It's free also, but it has that simple, basic and absolutely required feature for authenticating at an IMAP server: It's possible to enter an username! Wow.

I wonder how it is even possible that a big company like Microsoft does "forget" something like this in a product which Windows users are forced to use, after Windows Mail (which worked actually well so far) was purged suddenly, and I don't believe that this was a mistake. So better say good bye to "The new Outlook" and move on to an email client that is usable. Don't waste time with sending feature requests that are being ignored. because Microsoft don't WANT you to use their product for free anymore.

By the way you can also use Thunderbird with Office 365 and Live on many OS (not only Windows), and it does offer WAY more features than any Microsoft email client software did ever.