There can be two reasons for why you are seeing this error message that prevents you from enabling the Mailbutler Plug-In in Mail:

1. Your version of Mailbutler is outdated (Skip if not applicable)

The version of Mailbutler you are using is incompatible with your version of macOS. This is only the case if you are either using an outdated version of Mailbutler or a version of macOS that is incompatible with Mailbutler.

The Mailbutler Plug-In is compatible with macOS 10.13 High Sierra up to macOS 12 Monterey. If you are using one of these supported versions, please make sure you have the latest version of Mailbutler installed. Please note that upcoming beta versions of macOS are not guaranteed to be compatible with Mailbutler until they are officially released.

How to check for the latest version of Mailbutler:
1. Find and open the Mailbutler app in your Applications folder

2. Choose "Check for Updates" from the menu bar (or for older versions of Mailbutler from the Settings button in the lower-right corner of the window):

3. Confirm that you are seeing the following dialog and that the version shown matches the latest version indicated on If your version does not match, please download the latest version of Mailbutler from here.

2. Mail's Plug-In Management got corrupted and needs to be fixed

All versions of the macOS Mail client have been having a bug in their Plug-In management that occasionally causes Mail to refuse loading the Mailbutler Plug-In, even if it is compatible with the version of macOS you are using. This is an issue especially happening after an upgrade of macOS as well as when restoring your Mac from a Time Machine backup.

In those cases, unfortunately, due to security restrictions from macOS, Mailbutler is unable to resolve the issue on its own and thus it requires manual actions made from you as the user.

This guide is suitable only for macOS 10.14 Mojave and 10.15 Catalina. If you are running a newer version of macOS, please see this article. If you are not sure which version of macOS you are currently using, please go to the Apple icon in the upper-left corner of your screen and choose "About this Mac":

Instruction Guide for fixing a corrupted Plug-In management in Mail

Due to security restrictions, the only way to fix a corrupted Plug-In management in Mail on macOS 10.14 and macOS 10.15 requires temporarily disabling the System Integrity Protection (aka as SIP). You can safely re-enable it later, after having applied the fix. (See the Disabling and Enabling System Integrity Protection article from Apple for more technical information about this.)

  1. Temporarily disable the System Integrity Protection (SIP) in macOS
    1. Restart your computer in Recovery mode by holding down Cmd ⌘ + R while booting up
    2. Launch Terminal from the Utilities menu

    3. Enter the command csrutil disable in the Terminal prompt:

    4. Hit Enter to execute the command. You should now see a message confirming that System Integrity Protection was successfully disabled.

    5. Restart your computer
  2. Go to the Finder and from the menubar choose "Go" -> "Go to Folder…" (Cmd ⌘ + Shift ⇧ + G), then copy and paste the following path into the text field: ~/Library/Containers/ (make sure to include the ~ symbol at the beginning of the path):

3. Click the "Go" button. You should now see a DataVaults folder in the Finder window:

4. Move the DataVaults directory to the Trash, then empty it:


5. Restart Mail and try enabling the Plug-In again. If you still keep seeing the same error message, please contact our support.

6. Finally, re-enable System Integrity Protection by repeating the steps 1.1 to 1.5, except for the Terminal command which has to be csrutil enable, to revert the disabling of the System Integrity Protection.