outlook 2013 opens with error message "The operation failed. The messaging interfaces returned an unknown error."

Hi Saleem,

Welcome to Microsoft Office Community and thanks for posting the question.

Let us open outlook in safe mode and verify results:
1. Press the Windows + R key on the keyboard.
2. Type Outlook /safe (Leave a space after Outlook) -> Click OK.

If Outlook safe works, then refer the following link on how to disable add-ins in Outlook:
http://office.microsoft.com/en-in/excel-help/work-with-office-safe-modes-HP010354300.aspx

I hope the steps provided above fixes the issue. If not reply and I will be happy to help you.

Thank You

Hi Srinivasu,

After disabling Windows Search Email Indexer add-in, the error message disapper while opening outlook.

But user needs this search email indexer for instant search. Please let me know, how to keep this add-in without the error message while opening outlook 2013.

Thank you

Saleem Chandroth

i have the same problem with USER1 on outlook 2013 that connect to exchange 2010 , i tried make a new ost same problem but when i work with no cache that work fine , that problem appears on the USER1only , when i make a new User. user2 and configure it on same computer with cache that work fine! . when i switch to USER1 profile on Email and cache it i get this error message:

"The operation failed. The messaging interfaces returned an unknown error."

How do i fix it ?

I am having the same "Operation Failed" problem. This started with Win 10.

I tried the Outlook/safe mode but the message said that it could not find Outlook/safe.

Also email indexer is disabled.

This is driving me crazy.

What else can I try.

Thanks,  Alan

Thank you Hal. Outlook version is 2013.

Outlook account settings: Incoming imap.bell.net

Outgoing smtphm.sympatico.ca

I can now open outlook /safe.

Do you suggest that I use the "safe" mode for awhile and see if the "Operation Failed" appears agian?

Alan

Hello Alan,

Does Outlook work well in safe mode?

If Outlook works as expected in safe mode, disable the add-ins by following steps mentioned below and determine the problem causing add-in:

a) Click on File menu, click Options, Add-ins, Go button besides Manage: Com-in Add.
b) Check if there are add-ins listed, clear the checkbox.
c) Close the Office program and restart it.
d) Disable each add-in one at a time, restart the Outlook, and repeat the above procedure. If the issue reappears again, it will help you to determine which add-in is causing this issue.

Hope it helps. Reply with the result and I'll be happy to help you further.

Thank you.

Hello Alan,

Does Outlook work well in safe mode?

If Outlook works as expected in safe mode, disable the add-ins by following steps mentioned below and determine the problem causing add-in:

a) Click on File menu, click Options, Add-ins, Go button besides Manage: Com-in Add.
b) Check if there are add-ins listed, clear the checkbox.
c) Close the Office program and restart it.
d) Disable each add-in one at a time, restart the Outlook, and repeat the above procedure. If the issue reappears again, it will help you to determine which add-in is causing this issue.

Hope it helps. Reply with the result and I'll be happy to help you further.

Thank you.

Thank you for the suggestions. I have been working through your suggestion and I think (but one is never sure) that I may have found the culprit - gSyncit.  Will see as time goes on. Has anyone else had a problem with this ad-in. my Operation Failed trouble started when I installed Win 10.

Thanks again, Alan

On my case Outlook 2016, the Search Email Indexer was disabled for some reason, after enabling it I was able to send again. 

I use Google Apps Sync and a POP3 account on the same profile, I was not able to send emails from the POP/SMTP account for the last few days.