How to fix An internal server error occurred. the operation failed. Cannot send a message that is not marked as a draft or has already been submitted

Question

An internal server error occurred. the operation failed. Cannot send a message that is not marked as a draft or has already been submitted

Answer 1

The error indicates Outlook is trying to send a message that is no longer in a valid “draft” state. In the available information, similar “operation failed”/internal error issues when sending are caused by profile or server-side problems rather than something the user can fix inside a single message.

Based on the provided context, use these approaches depending on the scenario that matches best:

1. If the message is in Drafts in an on-premises Exchange environment and contains many inline images (for example, lots of colored bullets):
   • This is a known issue where the item is saved as read-only and sending fails.
   • Workaround for a single affected draft:
     1. Open the message from the Drafts folder.
     2. On the Ribbon, select Format Text.
     3. In the Format group, select Rich Text.
     4. Save and close the message.
     5. Reopen the message, go again to Format Text.
     6. Change the format back to HTML, then save.
     7. Reopen and send the message.
   • Permanent fix (for Exchange Server 2010 SP2 environments): install the update rollup described in KB 2785908 (Update Rollup 5 v2 for Exchange Server 2010 SP2).
2. If the error appears more generally when sending in Outlook and there is a mixed profile (Exchange + Google Apps Sync):
   • This configuration is known to cause “The operation failed. The messaging interfaces have returned an unknown error.” when sending.
   • Fix by separating accounts into different profiles:
     1. Create one Outlook profile that contains only the Exchange account.
     2. Create another Outlook profile that contains only the Google Apps Sync for Outlook account.
     3. Use the appropriate profile when starting Outlook.

If neither of these scenarios matches (for example, New Outlook for home with a consumer Microsoft 365 mailbox and no Google Apps Sync or on-premises Exchange), the issue is not covered in the provided material and requires further investigation outside this context (for example, checking add-ins, trying Classic Outlook, or recreating the profile).

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References:

• "The operation failed" error in the Outlook client when you open a saved message from the Drafts folder and then try to send it in an Exchange Server 2010 environment
• The operation failed error when you send email messages in Outlook