Why I cant add new email account in new outlook but in old it works?

Yep, exactly the same thing happened to me.

I have a work account and a university account, Windows installed and activated the 'new and improved' Outlook app. It defaulted to my uni account and got rid of my work account, then threw up this error.

Pathetic. Here's a thought, don't release something that isn't ready to be released. Here's what I want, to have all my relevant accounts on my computer, not to get forced into a fresh install that screws it up.

I found the 'try the new outlook' toggle, switching it off, and it's now allowing me to have multiple email accounts active.

Don't release things that aren't ready to be released, don't push the update on people, we are not your beta testers.

it seems to be linked to the type of license

i am an admin for multiple businesses and the only ones with issues are the exchange online licenses.

I have the same issue. The 'NEW' Outlook removed my Godaddy hosted 365 accounts and now says I cannot add them. I want my accounts back in Outlook.

Is there a way of reverting back to a previous version or Windows Mail?

I'm currently running into the same issue with one of our users.

Currently only a small handful of us (that I'm aware of) are using the preview. Myself & the user are both using emails from multiple tenants. For me it's 3 M365 accounts (and a gmail) and for him it's 4 M365 accounts, one of which is through GoDaddy, (and a gmail).

In our case, all of my accounts work. My accounts are licensed as MS Business Premium (x2) and Exchange Online 1 (x1). For my user, his WERE originally MS Business Premium (primary tenant) (x1), Exchange Online 1 (x2), and for the fourth tenant I don't have access but strong assumption he has MS Business Standard on that one. In his case, Tenant #1 (ms bus premium) and tenant #4 (godaddy, probably ms bus standard) function but the two exchange online accounts would not connect, claiming this same error. To clarify - my EO1 accounts DO work, and I changed his EO1 to an MS Business Premium license (upgraded him) and it did not change whether or not we could log into that account.

So it doesn't appear to be specific to licensing because it's not causing the issue for me & not resolving it for him. In both cases the master account was in our primary tenant which is MS Business Premium licensing. I am the admin in 3 out of the 4 tenants in question, and have not set anything to prevent users from using the preview. Additionally, no users have a flag set for OneWinNativeOutlookEnabled, however in testing I set this to true & it also did not resolve the issue.

Any input would be greatly appreciated.

I have the same issue. Switching to new Outlook disables all the Hosted Exchange accounts that I have on Microsoft 365 with the 'This account is not supported ....... message.

Im pretty sure this is a bug in coding. I just cant see that Microsoft would impose this licensing restriction on Outlook desktop users. After all, many people use Outlook to access third party email accounts so where would that leave them?

That having been said - Id add my voice to those requesting that MS fix this quickly and also explain how we can manually trigger a download of the latest build.