Shared Mailboxes make it possible to centralize email for a specific group of employees. If you don’t know what a shared mailbox is, think about the “Contact Us” address most web pages have. Or your company’s “Support” mailbox. Exchange implements these very easily through mailbox delegation. Grant users full access to the mailbox in the Admin Portal and the mailbox will appear in Outlook.
There is, however, a major flaw in how Exchange manages messages sent using the email address of a shared mailbox. If you send email with a shared mailbox, the message gets saved to your sent folder. This can be a huge problem for auditing and data retention efforts. This problem has existed in Exchange since Server 2003, and MS has chosen not to do anything about it, until Microsoft began formally implementing “Shared” mailboxes in Office 365.
A few years back, Microsoft finally fixed the sent items storage issue with a new option in PowerShell. This setting can be enabled using the set-mailbox cmdlet, as seen here:
set-mailboxsentitemsconfiguration -identity -sentitemscopiedto SenderAndFrom
Using the -sentonbehalfitemscopiedto switch to configure the same settings for emails sent on behalf of a user. And that’s all there is to it. You’ll need to get a list of mailboxes that need this setting, unless you’re making use of Shared Mailbox types, but this little change can save lots of time chasing down messages.