Hi,

GnuPG groups is a sometimes more unknown feature of GnuPG to allow a user to, when sending a mail to buglist@example.com, tell GnuPG that it shouldn't try to encrypt to that address, but rather to another address, or a list of addresses. 

This is typically used when either needing to explicitly override an encryption setting, or when encrypting to everyone on a small mailing list.

You specify it in gpg.conf like so:

  group buglist@example.com=joeblogs@example.com 36778025 missblogs@example.com

The number is a key ID, and you can specify either an email address or a key ID in the groups list.

In discussions with Werner Koch on how to implement this, it turns out that the groups feature is not visible throug gpgme, and the only way of implementing it is to call the GnuPG binary explicitly to get a list of groups.

I'm attaching here a patch to PGPCore which does the following:

 a) adds two new configuration options to Plugins/GPG:
     1) use_gpg_groups: to define if groups support should be enabled or not
        (default: not enabled)
     2) gpg_path: the path to the GPG binary.
 b) adds the function expand_gnupg_groups which takes a GSList ** of
    recipients and:
     1) imports the list of groups from GnuPG
     2) matches the groups to recipient addresses, and if finding a match,
        adding the group addresses to the list instead of the recipient address.
 c) adds a line to call expand_gnupg_groups from gpgmegtk_recipient_selection
    if use_gpg_groups is true.

Jonas