Outlook ‘Send As’ Permission Bouncing With 5.7.1: Mailbox Rights Fix

When you try to send an email as another user in Outlook, the message bounces back with a 5.7.1 error and a message that you do not have permission to send as that mailbox. This error occurs because the sending account lacks the required Send As permission on the target mailbox in Exchange Online or on-premises Exchange. This article explains the root cause of the 5.7.1 bounce and provides step-by-step fixes for both Exchange Admin Center and Exchange Management Shell methods.

Why the 5.7.1 Send As Error Occurs

The 5.7.1 bounce with the text “You do not have permission to send as this recipient” appears when an Outlook user tries to send a message from another user’s mailbox address. Exchange checks the sending user’s permissions on the target mailbox before allowing the message to leave the server. If the Send As permission is missing, Exchange rejects the message and returns the 5.7.1 status code.

This permission is distinct from Send on Behalf. Send As makes the message appear as if it came directly from the target mailbox owner. Send on Behalf adds “on behalf of” text in the From field. The 5.7.1 error specifically indicates that the Send As right is absent or misconfigured.

The most common cause is an incomplete delegation setup. Administrators often assign Send on Behalf permissions but forget to also assign Send As. Another cause is a permission change that has not replicated across all Exchange servers or has not been refreshed in the Outlook client cache.

Steps to Assign Send As Permission and Stop the 5.7.1 Bounce

You need Exchange admin permissions to complete these steps. The two methods below work for both Exchange Online and on-premises Exchange 2013, 2016, and 2019.

Method 1: Assign Send As Permission in Exchange Admin Center (EAC)

1. Open the Exchange Admin Center
   Go to https://admin.exchange.microsoft.com for Exchange Online. For on-premises, go to https://your-server/ecp. Sign in with an account that has Organization Management or Recipient Management role.
2. Navigate to the target mailbox
   In the left navigation pane, click Recipients then Mailboxes. Find the mailbox that the sending user wants to send as. Click the mailbox name to open its properties.
3. Open mailbox delegation settings
   In the mailbox properties window, click Mailbox delegation in the left menu.
4. Add the sending user to Send As
   Under Send As, click the + icon. In the dialog that opens, search for the sending user’s account name or email address. Select the user and click Add. Click OK to close the dialog.
5. Save the change
   Click Save at the bottom of the mailbox properties window. Wait 15 to 30 minutes for the permission to replicate across Exchange servers.

Method 2: Assign Send As Permission Using Exchange Management Shell

1. Open Exchange Management Shell
   On your Exchange server or admin workstation, open the Exchange Management Shell. For Exchange Online, connect using the Exchange Online PowerShell module: Connect-ExchangeOnline.
2. Run the Add-MailboxPermission cmdlet
   Type the following command and press Enter:
   Add-MailboxPermission -Identity "target@domain.com" -User "sender@domain.com" -AccessRights SendAs
   Replace target@domain.com with the email address of the mailbox you want to send from. Replace sender@domain.com with the email address of the user who needs the Send As permission.
3. Verify the permission was applied
   Run this command to confirm:
   Get-MailboxPermission -Identity "target@domain.com" | Where { $_.User -like "sender@domain.com" }
   You should see a row where AccessRights includes SendAs.

If the 5.7.1 Error Persists After Assigning Permission

Outlook still shows the 5.7.1 bounce after I assigned Send As permission

The permission may not have propagated yet. Exchange Online typically replicates within 30 minutes. On-premises Exchange can take up to one hour depending on replication latency. Close and reopen Outlook to force a cached permissions refresh. You can also clear the Outlook AutoComplete cache by going to File > Options > Mail and clicking Empty Auto-Complete List.

I assigned Send As but the From field still shows the original account

The sending user must manually select the target mailbox in the From field when composing a new message. In Outlook, click From in the message header, then click Other email address. Type the target mailbox address or select it from the Global Address List. If the From button is not visible, go to Options > Show From in the message window.

Send As permission works for some users but not others

Check whether the failing user has a different license type in Exchange Online. The Send As permission requires an Exchange Online license on the sending user’s account. Users with an Exchange Online Kiosk or Exchange Online Plan 1 license may need a higher license tier to use Send As. For on-premises, verify that the user mailbox is in the same Active Directory forest and that the permission object is not blocked by a security group.

Item	Send As Permission	Send on Behalf Permission
Description	Message appears to come directly from the target mailbox	Message shows “on behalf of” in the From field
Exchange attribute	Granted via Add-MailboxPermission with AccessRights SendAs	Granted via Set-Mailbox with -GrantSendOnBehalfTo parameter
Error on missing permission	5.7.1 bounce with mailbox rights error	No error, but recipient sees the delegation text
Permission scope	Per-mailbox, assigned to individual users or groups	Per-mailbox, assigned to individual users or groups

You can now assign the Send As permission using either the Exchange Admin Center or the Exchange Management Shell. After the permission replicates and the Outlook cache refreshes, the 5.7.1 bounce will stop. To verify the fix, send a test message from the sending user’s account while manually selecting the target mailbox in the From field. For advanced scenarios, combine Send As with Send on Behalf to give users both direct and delegated sending capabilities.