In Microsoft Exchange Server 2019 or Exchange Server 2016, consider the following scenario:
User A sends an email message to User B.
User B composes a reply by adding a S/MIME (Secure/Multipurpose Internet Mail Extensions) signature.
User B saves the reply as a draft.
In this scenario, you find that the draft of the reply does not have a value for the InReplyTo property.
To fix this issue, install one of the following updates:
Learn about the terminology that Microsoft uses to describe software updates.