Symptoms
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.
Cause
This issue occurs because new email messages aren't detected by existing search queries.
Resolution
To fix this issue, select one of the following cumulative updates to install on your computer:
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Cumulative Update 6 for Exchange Server 2016 or a later cumulative update for Exchange Server 2016.
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Cumulative Update 17 or a later cumulative update for Exchange Server 2013.
Workaround
To work around this issue, change IMAP4 search query (such as the casing) to detect new email messages.
Status
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
References
Learn about the terminology that Microsoft uses to describe software updates.