Using Shared Mailbox: This message could not be sent. You do not have the permission to send the message on behalf of the specified user.

Question

Error is [0x80070005-0x000004dc-0x00000524]

Answer 1

Hi Sniper IT,

Good day.

Thank you for your response.

According to your mentioned detailed scenario, this is little strange error message after assigning appropriate permissions.

I have consulted your situation with my team, and I would like to share more specific information with you, in order of your certain situation, the several things can be known and checked by backend side technical support team.

As an Office 365 global admin may need to contact our Office 365 technical support team on the back-end side via opening a service request so they can diagnose this specific scenario through some more technical resources, if needed, they may be collecting some different logs information from admin for further diagnosis. They can escalate this issue to the next level of the support team if it is required.

Since we forum moderators have limited permissions and access resources, due to this reason we are unable to collect certain detailed information in the public forum for data privacy. After diagnosing the scenario, our technical support team can provide possible information from their end.

If there is any known issue, our technical support team can provide from their backend resources.

For this standard process, here's the official document for the global admin: Get support - Microsoft 365 admin | Microsoft Learn (Online Option).

Important note: If any organization's Office 365 Business/Business/Education subscription is from a syndicated partner or reseller, and if the global admin can't open the service request on their end, they may need to contact the reseller's support provider so they can help the global admin to open the service request on their end. after the Office 365 support team will involve in the created service request.

Your cooperation precious time is highly appreciated.

Sincerely

Vaidya Darpan

Answer 2

Hi Sniper IT,

Good day.

Thank you for reaching out to Microsoft community.

Before moving forward, could you please allow me to collect following information to avoid some misunderstanding?

May I please re-confirm whether this mailbox account is Shared mailbox which is created by global admin or any user has shared their mailbox with you?

According to your too short description and error message "Using Shared Mailbox: This message could not be sent. You do not have the permission to send the message on behalf of the specified user"

It looks like you have not appropriate permission to send email from this affected shared mailbox account. If you are end user, you will need to contact Office 365 global admin in your Business organization and request them to assign or delegate Send As and Send on Behalf permission under the related shared mailbox account from admin portal.

Here is official document which applicable for Office 365 global admin: Create a shared mailbox - Microsoft 365 admin | Microsoft Learn

Below screenshot information has been captured from official document:

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Please note that I have provided above information based on your provided error message. If my understanding is not correct and your situation is totally different, you will need to feel free to correct me with some more brief information situation.

Initially, I was unable to find some more brief information situation in your topic description so that we can both understand particular situation. To better understand the specific situation, I have asked the information as a reconfirmation.

The reason for the above question is, different Microsoft account and subscription have different service and process, due to this reason, initial stage I have asked some question.

I will be waiting for your next update on this requested information so that certain things can be understood more clearly. I will provide you with more information and guidance according to the information you will provide in your next reply.

I would very much appreciate your valuable cooperation and precious time.

Sincerely
Vaidya Darpan

• I (it@.ca) am a Global Admin for Microsoft 365 Azure AD.
• I created the shared mailbox (testshared@.ca) in Exchange 365 Admin online.
• I granted it@.ca 'Send As', and 'Read and Manage (Full Access)' to myself for shared mailbox testshared@.ca in Exchange Online (EXO)
• I removed mailbox permissions as per the link above
• I then added mailbox permissions as per the link above
• $mailboxsharedname below is testshared@.ca
• I have set-mailbox $mailboxsharedname -MessageCopyForSentAsEnabled $True
• I have set-mailbox $mailboxsharedname -MessageCopyForSendOnBehalfEnabled $True
• I have set-mailbox $mailboxsharedname -GrantSendOnBehalfTo @{add="it@.ca"}

Looking forward to any information you may provide.

Answer 3

Hi Sniper IT,

Good day.

Thank you for reaching out to Microsoft community.

Before moving forward, could you please allow me to collect following information to avoid some misunderstanding?

May I please re-confirm whether this mailbox account is Shared mailbox which is created by global admin or any user has shared their mailbox with you?

According to your too short description and error message "Using Shared Mailbox: This message could not be sent. You do not have the permission to send the message on behalf of the specified user"

It looks like you have not appropriate permission to send email from this affected shared mailbox account. If you are end user, you will need to contact Office 365 global admin in your Business organization and request them to assign or delegate Send As and Send on Behalf permission under the related shared mailbox account from admin portal.

Here is official document which applicable for Office 365 global admin: Create a shared mailbox - Microsoft 365 admin | Microsoft Learn

Below screenshot information has been captured from official document:

=================================================================================================

Please note that I have provided above information based on your provided error message. If my understanding is not correct and your situation is totally different, you will need to feel free to correct me with some more brief information situation.

Initially, I was unable to find some more brief information situation in your topic description so that we can both understand particular situation. To better understand the specific situation, I have asked the information as a reconfirmation.

The reason for the above question is, different Microsoft account and subscription have different service and process, due to this reason, initial stage I have asked some question.

I will be waiting for your next update on this requested information so that certain things can be understood more clearly. I will provide you with more information and guidance according to the information you will provide in your next reply.

I would very much appreciate your valuable cooperation and precious time.

Sincerely
Vaidya Darpan