Cannot send from Shared Mailbox

Question

I am not a power user and just for small business and personal use. I am using Admin on the web for O365 and Windows Outlook. First question ever on this forum as usually, I can work out what I need.

I just wanted to set up a shared folder/inbox with a new name at my domain. Went through the whole process and all good and a new Folder appeared eventually and I went back in and set up permissions on the O365 Admin Center by going to the Shared Mailboxes, clicking on the shared inbox name and going through all the permissions.

I have tried deleting the shared email from the 'From' list when sending and typing in fresh, and showing on Global Address book is on. Tried tests numerous times and all set up over 20 hours ago. I have also sent emails from my main account the shared inbox email address - none received at all.

Doing a test email I get this response in my main inbox - I just cannot work out what the issue is and tried everything I could find on the web at least once.

Many thanks

Your message did not reach some or all of the intended recipients.

  Subject:	Test

  Sent:	28/02/2026 09:10

The following recipient(s) cannot be reached:

  Kevin Murphy on 28/02/2026 09:10

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

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Diagnostic information for administrators:

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

Exchange response headers:

request-id: 90b269bf-31ac-b8f4-c21b-6f97dd19fd0d

X-ServerApplication: Exchange/15.20.9654.014

X-FEServer: LO2P265CA0285

X-CalculatedBETarget: VI0PR07MB10601.eurprd07.prod.outlook.com

X-RequestId: {581B057D-436A-401C-BF85-8636A65D72DE}:62

X-ClientInfo: {4AF7845E-AE87-41E7-A739-3A8FE5B3C5EA}:60280052

X-ElapsedTime: 162

X-BackEndHttpStatus: 200

X-ResponseCode: 0

X-RequestType: Execute

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ROPs Summary:

0: ropSetProps (10) Processed(1) Completed(0)

	ROP result: 0

	Response codes: 0

1: ropSetProps (10) Processed(1) Completed(0)

	ROP result: 0

	Response codes: 0

2: ropFlushRecipients (14) Processed(1) Completed(0)

	ROP result: 0

	Response codes: 0

3: ropSetProps (10) Processed(1) Completed(0)

	ROP result: 0

	Response codes: 0

4: ropTransportSend (74) Processed(1) Completed(0)

	ROP result: 0

	Response codes: 1244

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Response Exceptions:

ROP Index: 4

ROP Associated: ropTransportSend (74)

Microsoft.Exchange.Data.Storage.SendAsDeniedException: Can't send message.

---> Microsoft.Mapi.MapiExceptionSendAsDenied: MapiExceptionSendAsDenied: TransportSend operation has failed (hr=0x80070005, ec=1244)

..., 2.54258:00000000, 0.40002:22000000, 1.56562:00000000, 1.33010:0A000000, 2.54258:00000000, 0.40002:22000000, 1.56562:00000000, 1.64146:0E000000, 1.33010:0E000000, 2.54258:00000000, 1.33010:0E000000, 2.54258:00000000, 1.64146:4A000000, 1.33010:4A000000, 2.54258:DC040000, 1.33010:4A000000, 2.54258:DC040000, 255.79500:302E3936, 0.100684:31343A56, 255.66700:30374D42, 5.95292:67000000446F526F70730054, 8.111356:D918340F51E07A00CAA1876E5DE77057A6536B31, 0.38698:AB037096, 1.107996:01000000, 1.41134:86000000, 0.124060:01000000, 1.41134:86000000, 0.124060:2C000000, 1.41134:86000000, 0.124060:86000000, 0.29756:00000000, 1.104236:00000000, 1.87852:00000000, 1.120620:00000000, 1.75564:00000000, 5.108332:000000004D6F4D5400000000, 6.64024:1A0104800300140E00000000, 4.41064:1A010480, 1.104236:00000000, 1.87852:00000000, 1.120620:00000000, 1.75564:00000000, 5.108332:000000004D6F4D5400707469, 6.45653:050007804000073000000000, 4.41064:05000780, 1.104236:00000000, 1.87852:00000000, 1.120620:00000000, 1.75564:00000000, 5.108332:000000004D6F4D5400343A56, 6.64024:1A0104800300161000000000, 4.41064:1A010480, 1.104236:00000000, 1.87852:00000000, 1.120620:00000000, 1.75564:00000000, 5.108332:000000004D6F4D5400000000, 6.45653:050007804000083000000000, 4.41064:05000780, 1.104236:00000000, 1.87852:00000000, 1.120620:00000000, 1.75564:00000000, 5.108332:000000004D6F4D5400000000, 6.45653:050007801F00FA3F00000000, 4.41064:05000780, 1.104236:00000000, 1.87852:00000000, 1.120620:00000000, 1.75564:00000000, 5.108332:000000004D6F4D5400000000, 6.64024:1A0104800201E26500000000, 4.41064:1A010480, 1.104236:00000000, 1.87852:00000000, 1.120620:00000000, 1.75564:00000000, 5.108332:000000004D6F4D5400000000, 6.64024:1A0104800201E36500000000, 4.41064:1A010480, 0.124060:00000000, 0.124060:00000000, 1.41134:86000000, 0.124060:00000000, 1.41134:46000000, 1.125148:00000000, 7.100572:020000000000000000000000, 1.121052:42000000, 1.75996:03000000, 1.92380:00000000, 1.108764:04000000, 1.122492:86000000, 5.40542:84B1C7164F666669636554776F466163746F7241757468202864333539306564362D353262332D343130322D616566662D6161643232393261623031632C33343432316662652D663130302D346535622D396334362D326665613235616137623838292E5047535F524D5000, 0.37692:00000000, 0.37948:00000000, 5.33852:00000000534D545000000000, 5.56248:DC04000053656E64417320636865636B206661696C65642062656375617365204149206973206E756C6C0000, 7.40748:010000000000010B00000000, 7.57132:000000000000000000000000, 4.39640:DC040000, 1.63016:4A000000, 8.45434:4C96728C8E7EF74DB6CD2029F977F9E300000000, 0.104348:00000000, 5.46798:130000004E6F745365745F4D6F4D540000000000, 7.51330:237F9C19A976DE0800000000, 5.10786:0000000031352E32302E393635342E3031343A564930505230374D4231303630313A66326365646630312D323434372D346566632D386432662D3938373137383864383762363A3338343536383A2E4E455420382E302E3234000000, 0.39570:00000000, 1.55954:0B000000, 0.40818:02000000, 1.33010:0B000000, 2.54258:00000000, 0.59634:02000000, 1.56562:00000000, 1.33010:0B000000, 2.54258:00000000, 0.59634:9F000000, 1.56562:00000000, 1.55954:0A000000, 1.33010:0A000000, 2.54258:00000000, 0.40002:0C000000, 1.56562:00000000, 1.33010:0A000000, 2.54258:00000000, 0.40002:00000000, 1.56562:00000000, 1.55954:0A000000, 1.33010:0A000000, 2.54258:00000000, 0.40002:22000000, 1.56562:00000000, 1.33010:0A000000, 2.54258:00000000, 0.40002:22000000, 1.56562:00000000, 1.64146:0E000000, 1.33010:0E000000, 2.54258:00000000, 1.33010:0E000000, 2.54258:00000000, 1.64146:4A000000, 1.33010:4A000000, 2.54258:DC040000, 1.33010:4A000000, 2.54258:DC040000, 255.97900:0A000000, 4.108172:DC040000, 1.52466:02000000, 1.52466:02000000, 1.42738:0C000000, 0.37698:07000000, 1.42738:0C000000, 0.37698:07000000, 0.60402:00000000

at Microsoft.Mapi.Managed.MapiExceptionHelper.ThrowIfError(LID lid, IHandle objectHandle, String message)

at Microsoft.Mapi.Managed.MapiMessage.Implement_TransportSendM

Transport-Send failed: failure enum(25), HResult(0x00000000), EC(1244).

Transport-Send failed: failure enum(22), HResult(0x00000000), EC(1244).

Submit-Message failed: message id(4), failure enum(13), HResult(0x80070005), EC(1244).

Answer 1

Hello Kevin,

Thank you for reaching out to Microsoft Q&A. The exact error you're seeing "You do not have the permission to send the message on behalf of the specified user" + SendAsDeniedException + error code 0x80070005-0x000004dc-0x00000524. It almost always means one (or both) of these two things:

1. You have Full Access (Read and manage) permission, but not the separate Send As permission.
2. The permissions haven't fully replicated yet in Microsoft's backend (this can sometimes take longer than expected, even up to 20 hours).

Full Access lets you see and read the shared inbox. Send As is what actually lets you send from it (so the email shows as coming from the shared address, not "on behalf of"). Quickest fix is to grant proper permission:

1. Go back to the Microsoft 365 Admin Center.
2. In the left menu: Teams & groups > Shared mailboxes.
3. Click your shared mailbox name.
4. Click Manage mailbox permissions.
5. Scroll down to the Send as section (it's separate from "Read and manage").
6. Click Add permissions > search for and add your own account > Save.

(Do the same for anyone else who needs to send from it.)

REF: https://learn.microsoft.com/en-us/microsoft-365/admin/email/configure-a-shared-mailbox?view=o365-worldwide#add-or-remove-permissions-of-members

https://learn.microsoft.com/en-us/troubleshoot/exchange/mailflow/cannot-send-email-with-full-access

Wait at least 30–60 minutes, sometimes up to a few hours for full replication.

Hope this help.

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