When I go to add my Office365 Enterprise account, it opens a page asking me to login. When I type in my username, the page complains that the account does not exist.
When I open up, for example, office.com and sign in through there, it works fine. I have double-checked the settings and they are all correct that I can see.
It may be the auth API on the backend has changed or is different in some way? Would be happy to purchase this software on the spot if this issue was fixed quickly.
I have the exact same problem. I was able to import all data from my current setup in Thunderbird on different email backend (Zimbra mail) but the Office 365 Enterprise account just won’t work.
I was wondering if you setup the account as IMAP (or Exchange), if that would work, as it won’t use 0Auth.
Go to Menu > Tools > Accounts, and delete the existing account. Instead of adding the account again using Automatic Setup, go to Mail > Other.
After entering your email address, make sure you have IMAP selected, and complete the setup.
If you want your contacts and calendar, it might be better to setup the account as Exchange.
I followed your instructions and the account was correctly generated. I was able to sync my inbox. Is there any way to do the actual importing from my current client (Thunderbird) in order to have all the folder structure I had previously setup in Thunderbird?
Yes, I tried through the exchange option as well. It didn’t work.
Scratch that, I didn’t realise you were suggesting adding the entire thing manually. This looks like it has worked. Thank you!
For anyone else, you may have to tick the ‘Ignore test results’ check box to get past the SMTP test. Then edit the account to adjust the settings:
IMAP: outlook.office365.com
Use SSL/TLS on Special Port (legacy) (port 993)
Username will be your office365 email address
SMTP: smtp.office365.com
Force usage of SSL/TLS (port 587)
Tick server requires authentication, use same as IMAP.
Yes, sometimes the autodiscovery of the security policy doesn’t work so well. Thanks for adding that Stephen. 
Yes, you can import from Thunderbird.
Go to Menu > File > Import > Thunderbird.
Rather than importing the whole thing, which will attempt to recreate the accounts, choose Import Selected Folders. Then select the folders you want to import and the destination.