outlook messaging interfaces have returned an unknown error

Hello, I'm Diane, an M365 Apps & Services MVP specializing in Outlook.

That error on sending usually means the profile is correct - specifically the address book service. A new profile should fix it.

Go to File > Account Settings > Change profile and restart Outlook. Click Options then New and create a new profile. Does that solve the problem?

What type of email account do you have configured in Outlook? POP, IMAP, Outlook.com, or Microsoft Exchange? If IMAP do not delete the existing profile - you will lose the contents of any folder labeled 'this computer only' if you delete the profile before exporting calendar & contacts.

Hello Joe,

I’m an, Independent Advisor and Microsoft user like you. Thanks for posting the query here at this forum.

Could you please try following steps, Microsoft Outlook users often get a “messaging interface has returned an unknown error” message as pop up each time Personal Storage Table (PST) file is corrupted.

1. Restart MS Outlook
2. Repair an Outlook data file (.pst) file
3. Empty the Deleted Items Folder
4. Create New PST File The creation of a new PST file involves creating a new PST file and importing the information from the original PST.
   1. Exit Outlook completely, go to Start -> Settings and click Control Panel.
   2. Double-click Mail, go to Services tab, click Personal Folders, and click Remove.
   3. Click Add, go to the Available information services box, click Personal Folders, and click OK.
   4. Then type the user’s first name in the File name box, click Open, click OK twice, and exit Control Panel.
   5. Start Outlook, start working as usual, and check if the issue is resolved.
5. To install all the Office updates - https://support.microsoft.com/office/2ab296f3-7f03-43a2-8e50-46de917611c5
6. Open Run and Type "Outlook.exe /safe" and click OK

Kindly verify the detailed steps in below blog which would be useful for you. https://bobcares.com/blog/the-messaging-interface-has-returned-an-unknown-error/

Note: This is a non-Microsoft website. The page appears to be providing accurate, safe information. Watch out for ads on the site that may advertise products frequently classified as a PUP (Potentially Unwanted Products). Thoroughly research any product advertised on the site before you decide to download and install it

Hope this information would be useful to you. Please feel free to get back if you need any additional info.

Thank you! Ravikumar Help the next person who has this issue by indicating if this reply solved your problem. Click Yes or No below.

Is this Outlook for Windows?

yes it is