I'd like to check the attachments of outgoing mails from a certain mailbox.
If one of these rules fail, the outgoing mail must be blocked or forwarded to a supervisor.
We are now on Exchange 2013, but will be moving to Exchange Online probably this year.
Thanks in advance for your ideas on this.
You can follow the below steps to Identify sensitive information across many locations, such as Exchange Online, SharePoint Online, OneDrive for Business, and Microsoft Teams.
More Information can be found
below are some of the conditions that can be set for your DLP policy: