When you run repeated SEARCH BODY requests in the mailbox by using Standard IMAP4 Commands in a Microsoft Exchange Server 2013 or Exchange Server 2016 environment, newly delivered messages that are reported to the mailbox may not be returned in the search results.
This issue occurs because new email messages aren't detected by existing search queries.
To fix this issue, select one of the following cumulative updates to install on your computer:
To work around this issue, change IMAP4 search query (such as the casing) to detect new email messages.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
Learn about the terminology that Microsoft uses to describe software updates.