Hi,
Which version of Exchange are you using?
"The problem exists only in one account regardless of the system he is using"
-So you have tested several devices with Outlook , right? Can the user login OWA without issue?
If there is only one mailbox affected, you can try:
1 move the mailbox to another database
2 export the mailbox to pst file, delete the mailbox, import the file to a new-created mailbox
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