I see a few others have also mentioned this issue. We're having big problems with inbound email delivery taking up to 24 hours and this morning we're now receiving issues with an error -

Your IMAP server wants to alert you to the following: Invalid credentials(Failure)

Nothing has changed our end, all the accounts that have been working fine until yesterday.

Can you please advise a resolution time?

As you would know many people rely on your email service for business so I would hope this has your highest attention.

Thanks,