IMAP is not supported for new Office 365 accounts.
My best info right now is still that some older accounts had IMAP, but they are going to lose it and be forced to ActiveSync exchange connections as they are migrated from older to new Office 365 servers.
If you ask about IMAP the Microsoft support moves the conversation to ActiveSync but they won't say or confirm in an email that IMAP ever existed or was taken away.