Comment by xorcist

IMAP supports a multitude of authentication standards, including hash and key-like, so the above is not necessarily true, however it is unlikely that Outlook supports them.

Client certificates are supported by both Thunderbird and K9, would prevent this type of issues.

In the cloud first era, your value is derived from how much customer data is under your control. Not for resale primarily but for stickiness. It's like the dot com era, only for real this time.