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Outlook 2019/2024

  • M

    Hello,

    I'm having a problem with a file attachment on four Outlook clients using Outlook 2019/2024.
    A file named Text.xlsx arrives in Outlook for four email accounts via the MDaemon Connector as "Untitled Attachment 01701.dat".
    However, it's displayed correctly as an Excel file in my Outlook.
    The four users can see the Text.xlsx file as an attachment via webmail.
    It seems to me that the incoming attachment isn't being decoded correctly in Outlook.
    If I copy the .MSG file to my mailbox on the MDaemon server, the email is displayed correctly in Outlook.
    An email I send to the email accounts containing the file .xls is displayed correctly as an Excel file in Outlook.
    I've already deleted the Attachments and localcache.db directories.
    The only remaining option seems to be deleting the Outlook profile.

    MDConnector 8.0.3
    MDaemon 26.0.1

    Martin

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  • A

    Please upload a copy of the MSG file from the recipients mailbox on the MDaemon server that the four users receive so that we can see the raw source of the email and attempt to replicate the issue. https://mdaemon.sharefile.com/r-rc3922c1eed334d4dbf5e34f0bd04ccd6

    However, it's displayed correctly as an Excel file in my Outlook.

    Are you using MDaemon Connector?  

     

    --
    Arron Caruth

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  • M

    I have uploaded the files.

    MDaemon Connector 8.0.3, MDaemon 26.0.1

    Martin

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  • A

    So far I have been unable to reproduce the issue.

    "Untitled Attachment 01701.dat" is being used because Outlook doesn't know the name of the file attachment.

    What email client is being used to send the message?  Whatever is generating the message is creating a malformed content type header for the attachment.  This is probably related to the issue.  

    Content-Type: application/application/pdf;

    What is the specific version of Outlook being used that is having the issue? You can check it by going to File | Office Account | About Outlook.

    Are all of the Outlook clients up to date? 

    Are the users that are having the issue also using MDaemon Connector 8.0.3?

    Is the option for download headers only enabled in MDaemon Connector?

    --
    Arron Caruth

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  • M

    The email originates from a Software Application responsible for sending it.
    I will contact the software vendor to report the error.

    The clients in use are:

    2x Outlook 2019 Build 10417.20117 and 3x Outlook 2024 Build 17932.20742.

    All clients are currently running version 8.0.3 from MDaemon Connector.

    No, download headers is not activated

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  • A

    Does MDaemon apply any content filter rules to the message while it is being processed?  

    If you edit the MSG file in the recipients mailbox and correct the Content-Type header, does the client display the attachment correctly?

    To do this you'll need to open the MSG file on the server in the recipients mailbox using your favorite text editor, I use Notepad++.  Find the Content-Type header that looks like this.

    Content-Type: application/application/pdf;

    And change it to look like this.

    Content-Type: application/vnd.openxmlformats-officedocument.spreadsheetml.sheet;

    Save the file, and then rename the MSG file.  Renaming the file will cause MDaemon Connector to see it as a new message so that it can be redownloaded.  The easiest way to rename it is to simply change the last digit in the name, you just have to make sure there is not another file already using the name.

    --
    Arron Caruth

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  • M

    Yes, the Mdaemon-Standard Rules.
    In addition, there is a Rule for MailStore, and a signature for specific addresses.

    I tested it: if I change the Content-Type, the file appears as .xlsx.
    The filename is "Untitled Attachment 01701.xlsx".
    The same email is sitting in my inbox; it displays correctly in Outlook, and within the MSG file, the Content-Type is listed as PDF.

    Martin

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  • A

    What language is the Operating System, Outlook, and MDaemon Connector of a machine that is having the issue?  Are all the same languages in use on your machine which is able to download and show the attachment correctly?

    Please upload a copy of MDaemon's  SMTP-In and Content Filter logs that show the message being received and processed so we can verify MDaemnon is not altering the message.  https://mdaemon.sharefile.com/r-rc3922c1eed334d4dbf5e34f0bd04ccd6

    What addins are being used in Outlook besides MDaemon Connector?  If you create a new Outlook profile on a machine that is showing the attachment incorrectly, disable all of the plugins except MDaemon Conenctor and allow it to download the message, does the attachment appear correct?

    --
    Arron Caruth

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  • M

    The operating system, Outlook, and MDaemon Connector are in German.
    Yes, the same language and version are installed on my computer, and they are displayed correctly.

    I have uploaded the log files.

    Begin Mon 2026-05-04 01:00:15.662: Session 13173967; child 0001
    End   Mon 2026-05-04 01:00:18.194: ----------

    The rule utilizing the content filter is the MailStore archiving rule.

    Only the MDaemon Connector plugin is being used.

    I removed the Outlook profile from the Registry and recreated it.
    The file on the computer still retains the filename "Untitled Attachment 01701.dat".

    Martin

    0 likes
  • A

    On a machine that has the issue, if you create a second profile as an IMAP account, not using MDaemon Connector, and have it download the message from MDaemon, is the attachment name displayed correctly?

    You can create a second Outlook profile by going to the Control Panel and selecting Mail.  There is an option to choose the profile when Outlook starts that can be temporarily enabled, which may make testing easier for you.

    What is the language for non unicode programs set to for the operating system of machines that have the issue and machines that do not have the issue?  This can be found by going to Settings | Time & Langauge | Language & Region, click the down arrow to the right for Windows display language.

    Is the option for Use Unicode UTF-8 for worldwide language support disabled?

    Are you viewing the message in the message preview pane or by double clicking the message to open it?

    --
    Arron Caruth

    0 likes
  • M

    I have added an IMAP account to Outlook, the attachment appears there as "Untitled Attachment 01701.dat".

    The Windows display language is German.
    The option "Use Unicode UTF-8 for worldwide language support" is disabled. This setting is also configured this way on my client, where the attachment displays correctly.

    I open the email by double-clicking it.

    0 likes
  • A

    I have added an IMAP account to Outlook, the attachment appears there as "Untitled Attachment 01701.dat".

    This indicates something other than MDaemon Connector is causing the issue.  The most likely issue is differences in Outlook MIME parser caused by minor variances in versions, but you've already confirmed version information.

    2x Outlook 2019 Build 10417.20117 and 3x Outlook 2024 Build 17932.20742.

    I would double check the versions and compare the version of the working and non working Outlooks.

    Any add-in / shim that touches messages on download. Outlook IMAP delivers into a local store; AV plugins, archiving plugins, DLP, mail filters can re-parse and reserialize. If the working workstations all have one of these and the broken ones don't (or vice versa), that explains the divergence even with vanilla IMAP profiles. List the COM add-ins on each:

      File → Options → Add-ins

    Settings worth checking, but unlikely to be the root cause

      - File → Options → Trust Center → Trust Center Settings → E-mail Security → "Read all standard mail in plain text" — affects body display, not attachment names, but rule it out.
      - File → Options → Advanced → International options — auto-select encoding etc. These affect outgoing messages and ANSI/Unicode property selection. The German display language is fine; the relevant detail was the system code page (1252).

    If you are still having the issue, lets make sure MDaemon is serving up the same data in both cases.

      1. On both workstations, set up the same vanilla IMAP profile against the same mailbox.
      2. Capture the wire trace for FETCH 1 BODYSTRUCTURE and FETCH 1 BODY[] for that message. Outlook has a built-in IMAP logger:
        - File → Options → Advanced → "Other" → Enable troubleshooting logging → restart Outlook → reproduce → logs end up
      in %temp%\Outlook Logging\.
      3. Diff the responses. If the bytes coming back from MDaemon are byte-identical on both workstations and only one shows the bug, the parser itself is the variable, and you're confirming an Outlook build/channel split. Update Office on the broken ones and retest.
      4. If the bytes differ, then despite "same MDaemon" the server is responding differently to the two clients — possible if e.g. one client is negotiating different IMAP capabilities, has a different login, or is hitting a cached vs uncached path.

     

    --
    Arron Caruth

    0 likes
  • M

    Let's stick to just two clients, both running the same version of Outlook 2019 (Build 10417.20117).
    The operating system is Windows 11 Pro, fully up to date.

    As previously mentioned, the "Test.xlsx" file arrives correctly on my client via the MDaemon Connector.
    Now, I have added the email account of the other user the one where it isn't working to my own client as an IMAP account.
    In Outlook, within this IMAP account, the email attachment appears as "Untitled Attachment 01701.dat".

    This is a single Outlook instance running two accounts; therefore, the attachment should theoretically display correctly in both accounts on my system.
    However, this is not the case in the IMAP account.

    What I find strange is this: if I copy the `.MSG` file from the other user's profile directory into my own mailbox, the email appears in my mailbox with the correct filename: `Test.xlsx`.
    If I then copy it back from my mailbox to the IMAP account, it once again appears as "Untitled Attachment 01701.dat".

    I simply cannot make sense of this :-(

    The settings on both clients under:

    - File → Options → Trust Center → Trust Center Settings
    - File → Options → Advanced → International options (auto-select encoding, etc.)

    are identical.

    The general Outlook settings on both clients are identical and correspond to the default settings.
    Even if I delete and then reconfigure the accounts on both clients, only my client works correctly after the setup is complete; the other client continues to display the attachment incorrectly.

    I have already uploaded the `.MSG` file via the provided link; could it be that the issue lies with the filename itself? Would you be able to check that?

    I extracted and decoded the BASE64 data, and everything appears correctly on my end including the filename and the `.xlsx` extension.

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  • A

    I have already uploaded the `.MSG` file via the provided link; could it be that the issue lies with the filename itself? Would you be able to check that?

    I've already checked the file name, I didn't find any issues with the file name itself.  The sending client is splitting the file name, but this should not cause an issue for Outlook or MDaemon Connector.  One MSG file is using pure ascii the other is using Charset iso-8859-1 for the file name.  I am unable to reproduce an issue with either MSG file.

    You uploaded two files, md5001000036528.msg and md5001000036529.msg, which MSG file is from the mailbox of the user that has the issue?  Or does the user account in question have issues with both? 

    Which MSG file are you testing in your account?  

    Why is the encoding different?  They are obviously two different messages, but I would expect the sending software to send the same way all the time.  

    Do thunderbird or eM Client have an issue with either MSG file when downloading it via IMAP?

    What does Outlook's debug logging show?  Are there any differences in what is logged between an Outlook that shows the file name correctly, and one that doesn't?

    --
    Arron Caruth

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