Dear CP-RMD,
Good day! Thank you for reaching out to Microsoft customer support.
I understand that you are experiencing an issue with the timestamp changing when you move emails from your main account sent items folder to subfolders within a shared mailbox account.
Please note that, this issue has been reported by Many users and our development team is currently working on a fix. However, currently as a workaround you can use Outlook on the web to move items from your main account sent items folder to shared mailbox folders/subfolders and keep the original timestamp of the email. I have been testing from my end and Outlook on the web isn't affected with this issue and it keep the original timestamp in the shared mailbox folders. Therefore, I will update this thread as soon as I get any additional information about the query and fix timeline.
Your patience, understanding and cooperation are much appreciated.
Thank you for your precious time. Have a nice day.
Sincerely,
Libeamlak | Microsoft Community Moderator