You send an email as the shared mailbox info@, but your colleagues can't see it: it's only in your own Sent Items. The result: two people answer the same customer, or nobody knows exactly what was promised. With one setting, Exchange Online also keeps a copy in the shared mailbox, so the whole team sees what has already been answered. This article shows how to set it up in the admin center or with PowerShell, and what to watch out for.
Why isn't the email in the shared mailbox?
A shared mailbox has no sign-in of its own. Outlook sends the message from your account, using Send As or Send on Behalf permission, and by default keeps the copy with you. Exchange Online can fix that at server level: for every message sent as or on behalf of the shared mailbox, it automatically adds a copy to that mailbox's Sent Items folder.
In the Microsoft 365 admin center
- Go to admin.microsoft.com > Teams & groups > Shared mailboxes.
- Select the shared mailbox.
- Next to Sent items, choose Edit.
- Tick Copy items sent as this mailbox and Copy items sent on behalf of this mailbox.
- Select Save.
In the Exchange admin center
- Go to admin.exchange.microsoft.com > Recipients > Mailboxes.
- Select the shared mailbox.
- In the details pane, open the Sent items settings. Depending on the version they're on the Mailbox or Others tab.
- Turn on both options: copy for sent as and for sent on behalf of.
- Select Save.
The exact wording can differ slightly between the Microsoft 365 and Exchange admin centers, but the result is the same.
With PowerShell
First connect with Connect-ExchangeOnline. For one mailbox:
Set-Mailbox -Identity info@contoso.com -MessageCopyForSentAsEnabled $true -MessageCopyForSendOnBehalfEnabled $true
For all shared mailboxes at once:
Get-Mailbox -RecipientTypeDetails SharedMailbox -ResultSize Unlimited | Set-Mailbox -MessageCopyForSentAsEnabled $true -MessageCopyForSendOnBehalfEnabled $true
Check the result with Get-Mailbox info@contoso.com | Format-List MessageCopyFor*. New shared mailboxes don't get the setting automatically: add it to your standard procedure or rerun the script regularly.
When does it work?
- When you send with Send As or Send on Behalf permission. How to grant those is in set up Full Access, Send As and Send on Behalf.
- It works for email sent from Outlook on the web, the new and classic Outlook and the mobile app, because Exchange makes the copy, not the app.
- The copy lands in the shared mailbox's Sent Items. A copy stays in your own Sent Items too.
- It only applies to messages sent after you turn it on. Older messages aren't copied.
Watch out with classic Outlook
Classic Outlook also has a registry value, DelegateSentItemsStyle, which puts the sent message in the shared mailbox instead of yours. Combine it with the Exchange setting above and you get two copies in the shared mailbox. Pick one method, preferably the Exchange setting: it also works in the new Outlook, where the registry value has no effect.
Common problems
- No copy appears: check that you're really sending as the shared mailbox. If your own address is in the From field, the setting doesn't apply. Here is how sending from another address works.
- Duplicate messages: see above, the registry value is probably set as well.
- It takes a while: after a change it can take a few minutes before it's active.
- Need replies to go elsewhere too? Consider email forwarding in Exchange Online.
FAQ
Do the copies count toward storage?
Yes, they take up space in the shared mailbox. Without a licence, a shared mailbox has a 50 GB limit.
Does it work for regular mailboxes too?
Yes. If an assistant sends on behalf of a manager, the manager sees what was sent in their name.
Does it work on my phone?
Yes. Read add a shared mailbox in the Outlook app.
Nederlandstalige versie: Verzonden items bewaren in een gedeeld postvak in Outlook