SEND AS permission needs reset on server side for Exchange

Hi @Lori Salow Marshall 

Thank you for confirming that you are working within a Microsoft 365 environment. 

Based on your description, it appears that the mailbox you are attempting to use as the sender in Classic Outlook is one for which you have been granted Full Access permission. However, this permission does not include the Send As capability. 

If your goal is to send emails from a different account in Classic Outlook without using Send As permission, the recommended approach is to add that mailbox directly to your Outlook profile as a separate account. This allows you to send messages from that account without additional permissions. For detailed instructions, please refer to: Add an email account to Outlook for Windows - Microsoft Support 

If your intention is specifically to send messages using Send As, I recommend reaching out to your organization’s IT administrator. They can verify whether your user account has Send As permission for the target mailbox by checking the Microsoft Admin Center or the Exchange Admin Center. Microsoft provides further guidance on this topic in the following article: Manage permissions for recipients in Exchange Online | Microsoft Learn 

Please note that these permissions are managed exclusively within your organization’s tenant and can only be configured by an administrator. 

I hope this information is helpful and assists you in moving forward. Please feel free to reach out and update me once you have had a chance to review this. 

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The MapiExceptionSendAsDenied error indicates a permissions issue on the mailbox, not something that can be fixed only on the Outlook client. However, the context shows that in many “Send As denied” scenarios the problem is caused by address caching or directory/permissions configuration, and can often be resolved without a full “reset” of permissions.

For a mailbox user (not a distribution group), confirm and correct as follows:

1. Verify Send As permissions on the server
   • In Exchange, confirm that the affected user still has the correct Send As permission on the target mailbox using the appropriate management tools (e.g., Add-RecipientPermission / Get-RecipientPermission were used in the documented scenario).
   • If necessary, remove and re‑add the Send As permission to ensure it is correctly applied.
2. Force Outlook to use the correct GAL entry
   • In Classic Outlook, create a new email.
   • Click From → Other Email Address.
   • In Send From Other E-mail Address, click From again.
   • Change the address book to the Global Address List (GAL) and select the mailbox that should be used for Send As.
   • This avoids using outdated, locally cached address information that can cause a Send As denial even when the server permissions are correct.

For a distribution group scenario where “Send As” or “Receive As” cannot be set or is denied due to access issues:

1. Check OU permissions for the Exchange Trusted Subsystem
   • Open Active Directory Users and Computers.
   • Enable View → Advanced Features.
   • Right‑click the OU that contains the distribution groups → Properties → Security → Advanced.
   • Add Exchange Trusted Subsystem as a principal.
   • Set Applies to = Descendant Group objects.
   • Clear all default permissions, then grant Modify permissions.
   • Apply and close all dialogs.
   • After this, reapply the Send As permission on the distribution group as needed.

If the account connects and syncs but cannot send, and local profile rebuilds are already done, the next steps are:

1. Confirm the Send As permission is present and correct on the mailbox or group.
2. Ensure Outlook is using the GAL entry (not an autocomplete or cached entry) for the From address.
3. For distribution groups, ensure the OU permissions for Exchange Trusted Subsystem are configured so that Exchange can correctly write and honor Send As permissions.

These server‑side checks and corrections, combined with selecting the From address from the GAL in Outlook, address the documented causes of Send As denied errors without requiring any additional client‑side fixes.

References:

• A user who has Send As permission can't send email messages as another user account in Outlook in Office 365
• Access denied when you try to give user "send-as" or "receive as" permission for a Distribution Group in Exchange Server