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Mozilla Thunderbird

 Thunderbird logo The Thunderbird mail client inherits a lot of it's bigger relative Mozilla Mail, but the small and fast bird has a feature set that makes it a worthy alternative.

Showing new mail in IMAP subfolders

The folders in your IMAP account will by default not be shown with the number of unread emails. You can change this through the user interface, but then these folders are not automatically monitored for the arrival of new mail. There is a user preference line that you can add to your personal user.js preferences file.
This file will not be overwritten by Thunderbird like the prefs.js file. Also, the preferences you set in user.js will override the same preference setting that might be present in the prefs.js file. The user.js file is located in ~/.thunderbird/????????.default/user.js where the ???????? string is a random set of 8 characters, derived by Thunderbird from your user name.

This is what you do:

  • Close Thunderbird
  • Open user.js in an editor (possibly that file does not yet exist, in which case you just create it)
  • Add this line to the file:
    user_pref("mail.check_all_imap_folders_for_new", true);
  • Re-start Thunderbird.

From this moment on, Thunderbird will also (periodically if you told it to) check the subfolders of your IMAP inbox.


Mozilla Mail and it's descendants like Thunderbird, are able to handle GPG-signed and/or encrypted emails with the help of the EnigMail extension. EnigMail uses your installed and configured GnuPG program files. So, you should have created a private and public GPG keyring or EnigMail won't work.
EnigMail takes care of transparently decrypting and encrypting your emails, as well as verifying signed emails automatically with a pre-defined GPG keyserver.

Adding GPG public key and fingerprint as custom headers to your outgoing emails

With Thunderbird, it is possible to add custom headers to each outgoing email. Mozilla Mail had this feature in a limited form - you could not automatically add a custom header with a default value.

We're going to profit from this feature by using it to add information about our GPG public key and fingerprint to each email we send, using these custom headers. Easiest is, to open your user.js personal preferences file called ~/.thunderbird/<profilename.default>/user.js in an editor and add the following lines:

user_pref("mail.identity.id1.headers", "gpgpubkey, gpgfingerprint"); 
user_pref("mail.identity.id1.header.gpgpubkey", "X-GPG-PUBLIC_KEY: http://pgp.mit.edu:11371/pks/lookup?op=get&search=0xA75CBDA0"); 
user_pref("mail.identity.id1.header.gpgfingerprint", "X-GPG-FINGRPRINT: F2CE 1B92 EE1F 2C0C E97E 581E 5E56 AAAF A75C BDA0");

Of course, the values are those of my own GPG key (0xA75CBDA0), you should fill in your own. Note, that I pointed the X-GPG-PUBLIC_KEY header to a GPG key server. This is where everyone should make his or her key available.
You can print the GPG fingerprint using one of the following commands (the first two will show you my own GPG fingerprint, the last one will show fingerprints for every entry in your personal GPG keyring):

gpg --fingerprint 0xA75CBDA0
gpg --fingerprint Eric Hameleers
gpg --fingerprint

If your Thunderbird profile contains more than one identity, you might have to copy the three lines above multiple times, substituting the id1 with id2, id3, and so on.

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