"5.7.1 smtp;550 5.7.1 RESOLVER.RST.AuthRequired" nondelivery report when external users try to send mail to mail-enabled public folders in Office 365

Note

Office 365 ProPlus is being renamed to Microsoft 365 Apps for enterprise. For more information about this change, read this blog post.

Original KB number: 2984402

Problem

When external users try to send email messages to mail-enabled public folders in Office 365, they receive a nondelivery report (NDR) that contains the following error code:

Remote Server returned '<xxxxxxxx> #5.7.1 smtp;550 5.7.1 RESOLVER.RST.AuthRequired; authentication required [Stage: CreateMessage]>'

Cause

By default, mail-enabled public folders are prevented from accepting mail from external senders. This behavior is by design and is intended to help protect mail-enabled public folders.

Solution

To change the behavior so that mail-enabled public folders can accept mail from external senders, follow these steps:

  1. Connect to Exchange Online by using remote PowerShell. For more info about how to do this, see Connect to Exchange Online using remote PowerShell.

  2. Add permission for the Anonymous account to public folders. To do this, run the following command:

    Add-PublicFolderClientPermission -identity <Public Folder> -User Anonymous -AccessRights CreateItems
    

    For example, run the following command:

    Add-PublicFolderClientPermission -identity "\SpecificFolder" -User Anonymous -AccessRights CreateItems
    

More information

For more information about mail-enabled public folders and Office 365, see Mail-enable or mail-disable a public folder.

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