Send as rights removed from shared mailbox

Jay Pluymaeckers 20 Reputation points
2025-11-17T12:54:09.8333333+00:00

Dear All,

Below you will find a case description:

In the afternoon of 14 november 2025, aliasses have been added to shared mailboxes. No other adjustments were made. Delegation has remained intact.

User "@domain.com" has access to shared mailbox "@domain.com" and "******@domain.com". As of the morning of 17 november 2025, when user A1 sends an e-mail with "from: ******@domain.com" they get a bounce back, invalid access rights. User no longer has "Send as" privilege.

Check Microsoft 365 tenant, Exchange Online Center and Powershell. All state that user still has delegated priviliges, "Full Access" and "Send as".

Resolution:

Remove delegated access. Wait 15 minutes, add delegation access. This did not resolve the issue.

Out of options, so do this again. Wait 15 minutes, now it works, but no idea why it worked the second time, but not the first time.

Questions:

1: How is it possible that the delegated privileges are suddenly on the back-end of Microsoft system no longer configured, even though all sources indicate that delegation is in order?

2: Is it possible to clarify why this happened?

3: Can anything be done to prevent this from happening? (Other than trial and error testing for days.)

Additional information:

On december 31st, adjustments will be made to the environment. Obviously, we will perform tests, however, we need to find out if this will happen again, especially since it took 3 days for the error to appear.

Adjustments to be made:

The aliasses mentioned above, will be configured to be primary e-mail addresses.

Exchange Online
Exchange Online

A cloud-based service included in Microsoft 365, delivering scalable messaging and collaboration features with simplified management and automatic updates.

0 comments
Answer accepted by question author
Jayden-P 26,285 Reputation points Microsoft External Staff Moderator
2025-11-17T14:54:04.3+00:00

Hi @Jay Pluymaeckers

Thank you for posting your question in the Microsoft Q&A forum.

Can you clarify if you saw this error message?

“This message could not be sent. Try sending the message again later or contact your network administrator. You do not have the permission to send the message on behalf of the specified user. Error is [0x80070005-0x0004dc-0x000524].”

Classic Outlook error when sending from Outlook.com "You do not have permission to send on beh…

If yes, you can consider using those work arounds mentioned in the article.

If this is not what you encountered, please provide the error message or screenshots so I can understand the issue better.

You mentioned you had to delegate the second time for it to work, this is likely due the changes didn't take effect right away. This process can take a while to make changes to the back-end service.

Delays in provisioning a user or mailbox - Exchange | Microsoft Learn

To identify the cause of this behavior, it would require Microsoft support to review your tenant's logs (via a service request with diagnostic traces from Unified Audit Log or Exchange transport logs).

However, this portal (Services Hub) is a paid ticket, which means you will need to pay in order to raise this ticket to the Support Team.

You can open a support ticket via Microsoft Unified Overview | Microsoft Unified 

To prevent this to happen again in the future, you can regularly check the Microsoft 365 admin center's Service Health dashboard for Exchange Online incidents, especially after making changes like alias additions.

I hope the information I provided will be helpful to you.

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  1. Jay Pluymaeckers 20 Reputation points
    2025-11-19T09:07:57.5133333+00:00

    Dear Jayden,

    That error message did not appear. I think it is best to just resolve this post. Everyone, including the dumb AI answer, seems to focus on the fact there was an error. This has already been resolved.

    I need to find the root cause of the issue, as the entire Microsoft 365 tenant was providing me with inacurate information, thus causing me to lose several hours in fixing the issue, which should have taken only 5 minutes if I had accurate information with regards to delegated access rigths no longer being available.

    Still, thank you for your time.

    Knd regards

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