Power Automate: send email from a shared mailbox, and fix the permission errors

Notifications from a flow look more trustworthy, and replies reach the whole team, when they come from a shared mailbox such as support@ instead of one person. Power Automate can send from a shared mailbox, but only when the right permission is in place, and the error when it isn't is confusing.

1. Pick the right action

Use Send an email from a shared mailbox (V2) when the team should see what was sent. Type the full address, such as support@contoso.com, rather than picking it from dynamic content, so the mailbox resolves reliably.

2. Get the permission right

The flow sends with its connection's account: whoever signed in to the Office 365 Outlook connection, not whoever triggered the flow. That account needs a permission on the shared mailbox, granted by an Exchange admin in the Exchange admin center (Recipients > Mailboxes > the mailbox > Delegation):

3. Fix the common errors

"You do not have the permission to send the message on behalf of the specified user"

• The connection's account doesn't have Send As yet. Ask an admin to grant it.
• It was granted recently. Microsoft says a new shared mailbox or permission can take about an hour to replicate. Wait, then run the flow again.
• The flow uses a different connection than you think. Open the action and check which account it shows.

"The specified object was not found in the store" or "Default folder Inbox not found" (on the trigger When a new email arrives in a shared mailbox (V2))

• The connection's account needs Full Access to the mailbox, not just Send As.
• A commonly reported fix: sign in to Outlook on the web as that account and open the shared mailbox once (Open another mailbox), then run the flow again.
• If it still fails, delete and recreate the Outlook connection, and select it again in the trigger.

The email never arrives

• Check the run history: if the action succeeded, look in the recipient's Junk and Focused folders, and in any Outlook rules.
• Sending lots of mail? The Office 365 Outlook connector allows far more calls than the older Mail connector, which is limited to 100 a day.

4. Replies and attachments

• Replies go to the shared mailbox, so the whole team sees them. To send replies somewhere else, fill in Reply To.
• Attachments: add them in the action's Attachments with a name and the file content. If the flow starts from an email in the shared mailbox, set the trigger's Include Attachments to Yes, or the content will be empty. See Files and attachments in flows.

Sources

• Microsoft Learn: Send an email from a distribution list or shared mailbox
• Microsoft Learn: Troubleshoot common issues with email in flows
• Microsoft Learn: About shared mailboxes: send permissions error
• Microsoft Learn: Issues triggering emails with attachments from a shared mailbox
• Microsoft Learn: Office 365 Outlook connector