I can't add a specific Office 365/Outlook account?
If you try to connect a different Office 365 account and you are always forced to select the same one, it’s a bug on Microsoft’s side, completely out of our control. The workaround is to log in to Missive and connect your Office 365 / Outlook account(s) from a private browser window.
Here’s how to do so (on a desktop computer, mobile is not supported):
2. Type mail.missiveapp.com in the address bar.
3. Log in to Missive.
4. Click your name in the lower-left corner of the window, click Accounts, then Add account.
5. Connect your account.
For each account, you may need to start over at step 1. Otherwise, the Microsoft popup may keep forcing you to select the account you previously selected.