Postbox 6 Upgrade Info

Welcome to Postbox 6!

We know you're going to love it!

This release is very different from previous Postbox releases, so we strongly recommend reading the following prior to installing Postbox 6.



While Postbox 6 may feel familiar, under the covers it has an entirely new foundation that will improve performance, message rendering, security, memory utilization, and reliability. A LOT has changed, so the installation instructions will be a bit different.

Migration Option

Postbox 6 installs into new data directories which allows it to run concurrently with older versions of Postbox. Your previous Postbox data folders will remain untouched on your hard drive.

If you have used version 3, 4 or 5 (within the last six months), Postbox will offer to migrate some (but not all) settings and data from your previous install to version 6.

During migration, Postbox 6 will:

  • migrate your account settings and passwords
  • migrate your POP and local mail
  • re-download IMAP mail from the server
  • migrate Filters, Signatures, Responses, Quick Posts, and Address Book data
  • migrate some (but not all) user preferences

Postbox 6 will not migrate:

  • many hidden preferences set using the Config Editor
  • add-ons (those have been discontinued, see below)
  • indexing data (a re-index will be required)

Clean Install Option

If you select "Clean Install" nothing will copy over! You will be starting from scratch.

If you select Clean Install by mistake, and now see nothing, don't worry! All of your original mail data is still intact! We simply need to re-migrate your settings, here's how:

  1. In Postbox 6, go to Preferences (macOS) or Options (Windows) > General, and select the checkbox for Show Profile Manager at startup.
  2. Restart Postbox, and it will enter into the Profile Manager. Create a new profile, give it a name, then start Postbox with that profile.
  3. When you reach the Migration Assistant, select the option to Migrate from Postbox 3, 4 or 5.

IMAP Limiting

Version 6 can now limit the number of messages that Postbox will fetch per folder. This feature is turned "ON" by default and is currently set at 2,000 messages (adjustable to 1,000, 2,000, 5,000, 10,000 or no limit). 

You can increase these limits so see more messages in Preferences (macOS) or Options (Windows) > Accounts > [your account] > Local Storage


Postbox is built using Mozilla code, and as of Firefox Quantum, add-ons are no longer supported by the Mozilla platform. Consequently, future versions of Postbox will no longer support add-ons, starting with Postbox 6.

Add-ons from Postbox, Inc. such as Cloud File Sharing, Signatures, and Responses are now available in the core Postbox 6 product.

Add-ons from 3rd parties will no longer operate as of Postbox 6.


Postbox 6 contains a new dictionary management system. To install a Mozilla dictionary, 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.

Hidden Settings

Most of the hidden preferences that customers have accessed through the Config Editor are now available in the UI. As such, we've removed the Config Editor from Postbox 6. We'll be adding more preferences to the UI over time.

Domain Fencing

We've adjusted the colors of our Domain Fencing feature. Grey addressing bubbles are the default, and red addressing bubbles will provide a warning if you're about to send to or from the wrong domain.

How to Purchase an Upgrade

If you purchased a Postbox 5 license key on or after March 1st, 2016, or a Postbox Lifetime Key on or before July 31st, 2010, then you already have a Lifetime License, and no purchase is necessary. Download and install Postbox 6, and you're good to go!

All other Postbox customers can upgrade to Postbox 6 by requesting a discount code. If you have any questions about purchasing or previous orders, please contact our Store.


1) Quit or Exit from Postbox so that it is no longer running.

2) Download and install Postbox 6 from here: 


3) If this is the first time using Postbox 6, you will be presented with an option to migrate settings from earlier versions of Postbox:

 Postbox Migration Assistant

Select "Postbox 3, 4, or 5" then select your desired profile. A clean install will set Postbox up with no previous settings.

Installing Additional Profiles 

The Postbox 6 migrator only imports one profile at a time, so if you would like to import additional profiles, here's what to do:

1) In the running profile, go to Preferences (macOS) or Options (Windows) > General and select the checkbox for Show Profile Manager on startup.

2) Restart Postbox, and you will launch into the Profile Manager. Follow the instructions for creating a new profile.

3) The Migration Assistant will reappear, allowing you to select a Postbox 3, 4, or 5 profile.

Postbox 6 FAQ

Do you have a PGP option?

Not at this time.

Will my favorite add-ons still operate in Postbox 6?

Postbox no longer supports add-ons.

Is it safe to remove the older Postbox directory after installing Postbox 6?

Postbox 6 installs into a new directory named PostboxApp. Instances of version 5 and below are located in a directory named Postbox.

We do not recommend removing anything from your hard drive unless absolutely necessary. But if you need to remove the older Postbox folders, you can find them here:


~ [your home directory] / Library/ Caches / Postbox
~ [your home directory] / Library / Application Support / Postbox