Outlook Emails Marked Out (Strike Though)

We have a user that is using Outlook 2016 as part of Office 365 with Exchange Online.  He has sent us a screen shot showing where about ten emails from a sender are marked out (strikethrough).  On a iMAP setup this means marked for deletion, but I don't believe that applies to an Exchange server.  Any ideas on why this happened?
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timgreen7077Exchange EngineerCommented:
The below article will help you with this and how to turn it off, but the email server may be an exchange server or any other message server, and IMAP is just ONE way to receive the emails:

grandrewAuthor Commented:
As I indicated, this is not an iMAP server, its an Exchange server.  That link does not seem to help.
timgreen7077Exchange EngineerCommented:
I suggest confirming that your user isn't using IMAP for accessing emails. As I mentioned, Exchange is your email server, and IMAP is ONE of the ways the emails are accessed. (NOT IMAP SERVER)
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grandrewAuthor Commented:
I have already checked.  I can 100% assure you he is not.
timgreen7077Exchange EngineerCommented:
then it's likely that the sender's set an expiration date on the emails

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Shaun VermaakTechnical Specialist/DeveloperCommented:
Check conditional formatting
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