Our app, mailstrom.co, connects to the Outlook IMAP server on behalf of many accounts. For some users, UID SEARCH is returning UIDs in non-ascending order; we are not able to process mail for these users. The condition seems to only affect certain accounts, and the same request always returns the same mis-ordered list of UIDs for that account.

See section 2.3.1.1 of RFC 3501 – "Unique identifiers MUST be strictly ascending in the mailbox at all times." http://tools.ietf.org/html/rfc3501

I can share with support the account names that have this condition. Thanks for helping to get this resolved.