Installing Dictionaries in Other Languages

Please note that Postbox does not yet support the web extension format, "webext." If a dictionary doesn't install for you, look for an earlier version of the dictionary that is NOT in the "webext" format. For example:

For the British Dictionary, use version 2.68.
For the German Dictionary, use version 2.06.

Visit the dictionary page, then click on "Version Information" at the bottom of the page, then click "See complete version history >>"

Select the latest version that is NOT "webext."


Instructions for Postbox 6 and 7

To install a Mozilla dictionary, visit the Mozilla Dictionary Page, download the dictionary to disk then go to Preferences (macOS) or Options (Windows) > Composition > Typing > Edit Dictionaries. Navigate to the downloaded dictionary file to install it.

Your default dictionary preference can be set in Preferences (macOS) or Options (Windows) > Composition > Typing > Language.

Within the Compose window, you can quickly switch between dictionaries for the current compose session by clicking and holding the Spelling toolbar button. Once you send, the dictionary will reset to its default language.

Instructions for Postbox 5 and below


  • Download and save the dictionary to your hard drive. (Firefox users, be sure to right-click the download link, then select "Save Link As..." from the contextual menu.)
  • In Postbox, go to Tools | Add-ons.
  • Click the Install button and select the file you downloaded and click "OK".
  • Restart Postbox and then go to Options >  Composition > Spelling and select your default dictionary.


For better integration with macOS, Postbox uses the system dictionary service and all of the dictionaries installed on your system.

To change the dictionary,

  • Go to Preferences > Composition > Spelling
  • Select your desired default language. You can also change this from the Spell check toolbar button in the compose window.

If Apple does not support a dictionary for your language, you can manually install additional dictionaries into your Operating System using the following steps:

  • Download and save the desired dictionary to your hard drive. (Firefox users, be sure to right-click the download link, then select "Save Link As..." from the contextual menu.)
  • Change the file extension from .xpi to .zip
  • Double-click the file to access the contents of the zip archive.
  • Under the dictionary subfolder in the zip archive, select the .dic and .aff files and copy them into <Your Home Folder> / Library / Spelling
  • Restart Postbox

This dictionary should now be available to the system dictionary service and will appear in the list of Postbox dictionaries.

Was this article helpful?
13 out of 22 found this helpful