Hi,
I understand that you have full access to the shared mailbox, and you'd like to recall the sent items but the option showing grayed out, right? If I misunderstand, please feel free to let me know.
In this case, please check how you opened this shared mailbox in Outlook client, as additional mailbox or as a second account.
Generally, we cannot recall messages sent through shared accounts. Recall only works if the account is opened as an account in Outlook. If the account was added to your profile as a secondary mailbox or as a managed or shared mailbox, recall is disabled,
even if you have Send as permission on the mailbox.
Hope this can be helpful.
Regards,
Aidan Wang
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