When I download the current Adobe flash player installer from the Adobe website using Safari 6.0.1 under OSX 10.8.2, I end up with a file named 'install_flash_player_osx.dmg.mdlp' in my downloads folder. I am curious as to why the .mdlp extension is being added to the disk image containing the flash player installer, which has always terminated with the .dmg extension in the past.

The only program which uses the .mdlp extension that I am aware of is matlab; matlab is installed on this machine and it is the program the OS would like to use to open the file. I have not seen OSX, or any component thereof, replace or append file extensions in the past and I am able to download .dmg files from other websites without this phenomenon occurring.

Note that I am not interested in suggestions regarding the opening of the file, but rather an explanation as to why the .mdlp extension is being applied in the first place, whether it be by the local machine or Adobe.

  • 3
    Hi dpddt! We do require you to post in English, and more than that, in correct English at least when it comes to capitalization and punctuation, especially if you already know how it works. Please respect that. I've removed the remaining comments for now. Thanks for your consideration.
    – slhck
    Oct 16, 2012 at 10:00
  • The same thing is happening on my machine, and I also have MATLAB installed.
    – Szabolcs
    Nov 27, 2012 at 18:06
  • I notice that no one has answered the question that the OP was actually interested in, namely, why is it happening? Nov 7, 2014 at 21:51

4 Answers 4


To fix this, just rename the file to not have the .mdlp extension, i.e. it ends in .dmg. Then, do get info on the .dmg file and change the "open with" to diskimagemounter, which should now be on the list of choices.


I did the following fix

  1. Use "Get info" on the file from Finder.
  2. Rename the file so it ends with .dmg only.
  3. Change the "open with" to diskimagemounter.
  4. Rename the file so that it ends with .dmg.mdlp again. Then it should work for all files...

Seems like it is an Adobe problem and not an OS X one. The "fix" is simply to remove the .mdlp extension from the file name as others have said.

From MacIssues:

Adobe distributes flash using a file management routine that appends the extension “.mdlp” to the file being downloaded. This routine is somewhat similar to the routine that Apple uses with Safari, where you will see the extension “.download” associated with files as they download.

For some reason, at times Adobe’s services will not change this appended extension before the file is handed off to your browser for downloading, so when Safari saves the file it will further append “.download” and then remove only this extension when done, resulting in the downloaded file being left with .mdlp as the final extension.

  • This is the only answer that addresses the OPs question about WHY the .mdlp extension is appended Mar 12, 2016 at 16:48

I'm experiencing the same issue, although not being able to solve it with the fix provided above. Instead, I directly try to open the .mdlp-file with another program, i.e., Open With -> Other, then locating DiskImageMounter under \System\Library\CoreServices, also making sure to check the box so that DiskImageMounter becomes default. Tada!

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