The operation failed error when you send email messages in Outlook
Original KB number: 3028159
When you send email messages in Microsoft Outlook, you receive the following error message:
The operation failed. The messaging interfaces have returned an unknown error. If the problem persists, restart Outlook.
This issue occurs when a Google Apps Sync for Outlook account and an Exchange Server account are configured in the same Outlook profile.
Don't configure an Exchange Server account and a Google Apps Sync for Outlook account in the same Outlook profile. Instead, create separate Outlook profiles, and then configure the Google Apps Sync for Outlook account in one profile and the Exchange Server account in another profile. This Microsoft Knowledge Base article describes how to create profile and set up an e-mail account in Outlook.
For more information about this issue, go to the Google Apps Known Issues page, and then expand the "Email Clients and Mobile Devices" section.
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