Shared Mailbox Sent Items: Keeping a Copy in Outlook

By default, sending “as” or “on behalf of” a shared mailbox in Outlook files the sent copy into your own mailbox’s Sent Items folder rather than the shared mailbox’s own Sent Items — making it hard for a team to see a shared record of what’s actually gone out from that address. A single registry DWORD fixes it, but the exact registry path depends on which version of Outlook is installed.

The Registry Fix

This must be applied while logged in as the specific user whose Outlook needs fixing (it’s a per-user, HKEY_CURRENT_USER setting, not machine-wide):

1. Press Start, type regedit, and open Registry Editor.
2. Navigate to the key matching your Outlook version (see table below).
3. Right-click the Preferences key, choose New > DWORD (32-bit) Value, and name it DelegateSentItemsStyle.
4. Double-click it, set the value to 1, and click OK.
5. Close Registry Editor and restart Outlook (a full reboot isn’t required, but a complete Outlook restart is).

Registry Path by Outlook Version

• Outlook 2007: HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Outlook\Preferences
• Outlook 2010: HKEY_CURRENT_USER\Software\Microsoft\Office\14.0\Outlook\Preferences
• Outlook 2013: HKEY_CURRENT_USER\Software\Microsoft\Office\15.0\Outlook\Preferences
• Outlook 2016 / 2019 / Microsoft 365: HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\Preferences

After restarting Outlook, send a test email from the shared mailbox and confirm it now appears in the shared mailbox’s own Sent Items folder rather than yours.

The Exchange Online Way to Do This Without a Registry Edit (Updated for 2026)

If the shared mailbox lives in Exchange Online (or current on-premises Exchange Server Subscription Edition), there’s now a server-side alternative that avoids touching the registry on every user’s machine at all. Two Set-Mailbox parameters control this behaviour directly on the shared mailbox itself:

Set-Mailbox <SharedMailboxName> -MessageCopyForSentAsEnabled $True
Set-Mailbox <SharedMailboxName> -MessageCopyForSendOnBehalfEnabled $True

Both parameters default to $False, so they have to be explicitly turned on. Once enabled, every user who sends as (or on behalf of) that shared mailbox gets their sent copy filed into the shared mailbox’s own Sent Items automatically — no per-machine registry edit needed, and it works for every delegate at once rather than one Outlook install at a time. The two mechanisms can interact if both are in play on the same mailbox. Microsoft’s own compatibility table is worth keeping handy:

DelegateSentItemsStyle	MessageCopyForSentAsEnabled	Result
0	True	Copy saved in both the delegate’s mailbox and the shared mailbox
1	True	Two copies saved in the shared mailbox, none in the delegate’s own mailbox
0	False	Copy saved in the delegate’s own mailbox only
1	False	Copy saved in the shared mailbox only (the original registry-fix behaviour)

One important caveat if you’re on new Outlook for Windows: it doesn’t read classic Outlook registry preferences at all, so the DelegateSentItemsStyle registry fix above simply has no effect there — the Set-Mailbox parameters are the only way to control this behaviour for new Outlook users. If your organisation has any users on new Outlook, the server-side route isn’t just more convenient, it’s the only option that actually works for them.