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Mikey_O's avatar
Mikey_O
Copper Contributor
Jun 25, 2024

Email sent from Shared Mailbox gets stuck in Outbox

Hello,   I am working with a client who has a primary and shared mailbox in Outlook. They are using the newest version of classic Outlook desktop app and they have full permissions to the shared ma...
exchange
office 365
outlook for windows
armandsalmon's avatar
armandsalmon
Copper Contributor
Sep 13, 2024
I am having the same issue and seeking a resolution. Like you, I thought I originally resolved this by removing data files and profiles within control panel > mail. I then re-added the primary account including shared mailbox. I was able to send as the shared mailbox for a few hours and prematurely celebrated.

Shortly after, I noticed that items are stuck in the outbox... and even stranger is that even though the profile and data files were removed, the outbox showed items stuck from before the data & profiles were removed. (they were not there when the accounts were re-added, but they came back somehow).
Mikey_O's avatar
Mikey_O
Copper Contributor
Oct 03, 2024

armandsalmon Hey, so we managed to get this resolved using the solution below. Since we applied this, it's been 2 months without issue. I hope this helps you as well.

 

Resolution

The issue was resolved (with Microsoft support help) by re-applying Full Access permissions and removing shared mailbox Outlook auto-mapping for the affected users and then adding the shared mailbox manually in Outlook. Re-applying permission via Office 365 admin centre didn't have any effect.

  • Launch Windows Power Shell as administrator and https://can01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.mysysadmintips.com%2Fwindows%2Fservers%2F373-connect-powershell-to-exchange-online-office-365&data=05%7C02%7CMike.Olejnik%40saultcollege.ca%7C3c662b4353344d1cd1ee08dcbbc281ec%7C9c61dd9d3b294f6db3b1f212de3c25da%7C0%7C0%7C638591691275807068%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C4000%7C%7C%7C&sdata=pd5Ecs6qk0h0J2zHahdvVayzK8783b0rqeMqOxGXYXc%3D&reserved=0.
  • Run: Remove-MailboxPermission -Identity mailto:email address removed for privacy reasons -User mailto:email address removed for privacy reasons -AccessRights FullAccess
  • Run: Add-MailboxPermission -Identity mailto:email address removed for privacy reasons  -User mailto:email address removed for privacy reasons  -AccessRights FullAccess -AutoMapping:$false
  • -AutoMapping:$false disables shared mailbox auto-mapping to users' Outlook profiles.
  • Wait 30-60 minutes for changes to propagate until shared mailbox disappear from users' Outlook.
  • Manually add shared mailbox to users' Outlook: File > Account Settings > Change > More Settings > Advanced > Open these additional mailboxes.
  • Try sending email as the shared mailbox by selecting From: address from Online Global Address List (to prevent caching issues).
  • TechCom1200's avatar
    TechCom1200
    Copper Contributor
    Dec 09, 2025

    Looks like they have improved the commandlet and you can achieve the same by doing this instead:

    Remove-MailboxPermission -Identity "HR Project" -ClearAutoMapping

    In Exchange Online, this example excludes the HR Project mailbox from auto-mapping in Outlook for all users who have Full Access permission to the mailbox.

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