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Outlook reply fails with "This is not a valid file name." error

Anonymous
2021-11-04T20:28:22+00:00

When replying to a certain a colleague's email I get the following error on send:

And also the following when I select save as:

  • This hasn't been an issue before a few days ago.
  • Myself and at least 1 other person have observed the exact same issue, but only when trying to reply to one specific person.
  • This error only occurs when using the desktop Outlook client, not the online client.
  • Restarting the pc and outlook doesn't help
  • Saving the original message (not the reply) doesn't cause any error.

I can't find any reference to someone else experiencing this error when trying to reply to an email. Please help if you have any ideas.

Outlook | Windows | Classic Outlook for Windows | For home

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  1. Anonymous
    2021-11-05T08:21:50+00:00

    Hi MattyMattyMatt

    Greetings

    Thank you for posting in Microsoft Community.

    Please let me know what version of Outlook you're using.

    Usually when one gets the error message saying the messaging interface has returned an unknown error, then it has to do with a corrupted PST file in your Outlook.

    Please try to use the Inbox repair tool (scanpst.exe) for instructions on how to do so, kindly refer to Repair Outlook Data Files (.pst and .ost) (microsoft.com)

    You may also try to run a repair on your Outlook and check to see if the issue still persists, Repair an Office application (microsoft.com)

    Lastly you may also try to Create an Outlook profile (microsoft.com)

    Please feel free to let me know how it goes.

    Kind Regards,

    Momo

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  1. Anonymous
    2021-12-01T22:43:46+00:00

    Has anyone found the issue with this? Doing a repair/re-install of Office, and repairing the pst file does not work!

    I believe it is linked to Azure Information protection tagging, as the user, we have this issue with, on the tagging of email, the description has a / in it when we don't have that in the description at all. So this is very odd!

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  2. Anonymous
    2021-12-22T14:03:02+00:00

    It has something to do with the specific content being forwarded. If you delete parts of that forwarded message, eventually the reply will proceed.

    I've noticed it twice, both times with eBay shipping updates being forwarded to me from another eBay account holder, and me replying to that person. I've traced it to a cell in a table, and it still does it after deleting all other content.

    This single-cell table gives the same error if you attempt to copy it, and you can't paste it into any of the other office programs. Strange.

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  3. Anonymous
    2021-12-03T17:56:57+00:00

    We just started seeing this issue. We also have AIP set up and deployed with the UL add-in in Outlook.

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  4. Anonymous
    2021-11-09T22:10:30+00:00

    Hi MattyMattyMatt

    I'm following up on this thread, any update?

    Thanks,

    Momo

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