Outlook 2019/2024

• M

  Martin

  4/27/26, 2:53 AM

  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

  Arron Admin Staff

  4/27/26, 8:57 AM

  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?  

   

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  Arron Caruth

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• M

  Martin

  4/28/26, 10:01 AM

  I have uploaded the files.
  
  MDaemon Connector 8.0.3, MDaemon 26.0.1

  Martin

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• A

  Arron Admin Staff

  4/28/26, 2:29 PM

  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?

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  Arron Caruth

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• M

  Martin

  4/29/26, 12:32 AM

  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

  Arron Admin Staff

  4/29/26, 6:23 AM

  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.

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  Arron Caruth

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• M

  Martin

  5/1/26, 3:11 AM

  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

  Arron Admin Staff

  5/1/26, 6:43 AM

  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?

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  Arron Caruth

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