Microsoft 365 – “This message could not be sent. The client operation failed. Try sending the message again later.”

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Sending messages from Exchange shared mailboxes is standard for businesses. Users may experience email delivery failure when sending messages as another mailbox with the following non-delivery report (NDR) examples:

This message could not be sent. Try sending the message again later, or contact your network administrator. Error is [0x80070005-00000000-00000000].

So what do you do when this happens? Here are a few troubleshooting recommendations and solutions to try.

Possible Cause: Broken Offline Address Book

When Outlook is set up in cached mode, the local address book copy can become corrupted for various reasons. And when that happens, it can also affect your Outlook’s ability to send messages from another mailbox.

Although less common in modern Microsoft 365 environments, a corrupted Offline Address Book may contribute to mailbox delegation and recipient resolution problems.

Solution 1: Force an update of the offline address book

1. In Outlook, click the Send / Receive ribbon group > Send/Receive Groups > Download Address Book.
   

   

2. Uncheck the Download changes since last Send/Receive box and click OK. Doing so means Outlook will rebuild the OAB files.
   

   

3. Wait for the OAB download to complete.
   

   

Solution 2: Delete the offline address book files

If the error persists, then it could be the OAB is beyond repair. In this case, you must delete the existing OAB file to have them recreated.

1. Close Outlook.
2. Locate the Offline Address Book files. The default location on Windows 7 and above is:
   

    C:\Users\Username\AppData\Local\Microsoft\Outlook\Offline Address Book

3. Rename the GUID-named folder. In this example, we’ll rename 6dc407a3-abbb-4f24-949c-fa669b396ba9 to 6dc407a3-abbb-4f24-949c-fa669b396ba9.old.
   Note. If you have multiple Outlook profiles set up, there will be an equal number of OAB folders.
   

   

4. Re-open Outlook, and the OAB folder will be recreated automatically.
   

   

5. Re-download the Offline Address Book.
   

   

   The Offline Address Book files have been recreated.
   

   

Possible Cause: Missing Send As Permission

The error 0x80070005 translates to a permission problem. Perhaps the user didn’t have the appropriate Send As permission to the mailbox. But if the user did, the permission may have been removed if the mailboxes were migrated from On-Premises to Exchange Online.

Solution 1a: Add Send As Permission via PowerShell

1. Open PowerShell and connect to Exchange Online. In case the Exchange Online PowerShell module is not installed, you need to install it first:
   

   Install-Module ExchangeOnlineManagement

   And then connect to Exchange Online using the command:

   Connect-ExchangeOnline

2. Run the following command to give Send As permission to the mailbox. In this example, the shared mailbox is Mailer365, and the user to have permission is AlexW.
   

   Add-RecipientPermission -Identity "Mailer365" -Trustee "AlexW" -AccessRights SendAs

   
3. Confirm that the permission is applied:
   

   Get-RecipientPermission -Identity "Mailer365" -Trustee "AlexW"

   

Checking Shared Mailbox Permissions

When troubleshooting shared mailbox access issues, you should check both mailbox access permissions and sending permissions.

In order to check Full Access permissions, run the command:

Get-MailboxPermission Mailer365 |
Where-Object {
$_.User -notlike "NT AUTHORITY\SELF"
}

The command above displays users who have mailbox access permissions assigned to the shared mailbox. If Send As permissions also need to be verified, use Get-RecipientPermission.

A user may have:

• Full Access but no Send As permission;
• Send As permission but no Full Access permission;
• both permissions;
• neither permission.

For shared mailboxes, Full Access and Send As permissions are configured independently and you should verify them separately.

To check if the user needs send as or send on behalf permissions, run the command:

Get-Mailbox Mailer365 |
Select-Object -ExpandProperty GrantSendOnBehalfTo

You can also verify Send As permissions with the following command:

Get-RecipientPermission Mailer365

Note that shared mailboxes support two different delegation models:

• Send As — messages appear as if they were sent directly from the shared mailbox.
• Send on Behalf — recipients see that the message was sent on behalf of the shared mailbox.

Here is an example:

From: Sales Team <sales@contoso.com>

indicates Send As.

From: John Smith on behalf of Sales Team

indicates Send on Behalf.

In case a mailbox is configured for Send on Behalf but the user attempts to send messages as the mailbox, Outlook may return permission-related errors. You should check if the assigned permission matches the intended delegation model.

Checking Microsoft 365 Audit Logs

If Send As or Full Access permissions were previously working and suddenly disappeared, you need to check the Microsoft 365 Audit Logs to determine if the mailbox permissions were modified/removed. Audit logs can help you to identify who changed the permissions and when the change occurred, which is especially useful after mailbox migrations/admin changes.

If you are using the modern Exchange Online PowerShell V3 module, you can also check if the permission has propagated with:

Get-EXORecipientPermission `
-Identity "Mailer365"

If the newly assigned Send As permission is not returned immediately, you should wait several minutes and run the command again, as Exchange Online permission changes may take some time to propagate.

Verify Shared Mailbox AutoMapping

In case the user has Full Access permission but the shared mailbox does not appear in Outlook, AutoMapping may not be working correctly. This can occur after mailbox migrations, permission changes, or Outlook profile issues. In this case, you need to try removing and reassigning the Full Access permission/manually adding the shared mailbox in Outlook.

You can verify Full Access permissions using the following command:

Get-MailboxPermission Mailer365

Keep in mind that AutoMapping affects how the mailbox is displayed in Outlook, but it does not grant Send As permissions.

Solution 1b: Add Send As Permission via the Admin Center

1. Log in to the Microsoft 365 Admin Center.
2. Navigate to Teams & groups > Shared mailboxes and select the shared mailbox from the list.
   

   

3. Under Mailbox permissions, click the Send as permissions link.
   

   

4. Click Add permissions.
   

   

5. Select the user(s) who will be given Send As permission and click Add.
   

   

6. Ask the user to wait to allow for propagation and try sending as the shared mailbox again. Note that permission changes in Exchange Online may take from several minutes up to 60 minutes to become effective.
   

   

Referer. Check our tutorial on how to add calendar permissions in Microsoft 365 via PowerShell.

Wrapping up

In most Microsoft 365 environments, error 0x80070005 is related to mailbox delegation/permission problems. You need to check Send As, Full Access, and Send on Behalf permissions first. In case permissions are configured correctly, you should investigate Outlook-specific issues (such as AutoMapping, Offline Address Book corruption, or profile-related problems).

Overall, by following these best practices and taking advantage of the built-in support resources provided by Microsoft 365, users can minimize the risk of encountering the “This message could not be sent” error and ensure that their email communications are as reliable and efficient as possible.