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

It seems that those who have the "Exchange Online (Plan 1)" license cannot use the New Outlook, because this plan only gives the right to use applications in the browser, and the old outlook does not validate this license, so we were able to use the old one.

To check what plan you have, go to Microsoft web "My Account" > "Office Apps" > "Subscriptions" and look for "Exchange Online".

Found here: https://answers.microsoft.com/en-us/outlook_com/forum/all/new-outlook-app-mail-and-calendar-substitute/2dcedbf9-880b-48bb-a020-0da738a00e64

It seems that those who have the "Exchange Online (Plan 1)" license cannot use the New Outlook, because this plan only gives the right to use applications in the browser, and the old outlook does not validate this license, so we were able to use the old one.

To check what plan you have, go to Microsoft web "My Account" > "Office Apps" > "Subscriptions" and look for "Exchange Online".

Found here: https://answers.microsoft.com/en-us/outlook_com/forum/all/new-outlook-app-mail-and-calendar-substitute/2dcedbf9-880b-48bb-a020-0da738a00e64

People keep coming to this conclusion, but look at my previous response (end of page 3), it for sure is not strictly based on licensing. My post goes over how 1) paying for higher tier licensing did not resolve the issue [by upgrading licensing for the account in question], 2) I have accounts on Exchange Online 1 licensing which DO work in the new app.

It does not appear to be exclusive to licensing.

That is not correct. At least your description as to where to verify your license is not correct,. The only subscription I have is to Office 365 which is only the office suite and not email. My 365 email account was purchased through GoDaddy and managed by them as well. Here's the rub... it USED to work, and now it doesn't. Some engineer broke something while attempting to fix something else. Each build introduces new issues, and it's MADDENING. Why couldn't they just repair windows mail? That's another piece of software that got progressively worse as they tried to fix things. It finally got to the point that you couldn't even add a Yahoo account without an error. The new outlook had promise initially, and all they really had to do was fix it so the read/unread flag got changed on the email server when it was read in outlook. IMAP is supposed to do that on the fly, right? Instead, MS broke something else which disables their own exchange mail from even being added!

Why can't MS get email right? They blew it with Bing (Google Maps), IE/Edge (Chrome), and now email, which will probably be handled by Gmail unless MS gets their act together. This is a bad joke at this point.