This Plugin makes Roundcube webmail http://roundcube.net/ show the encrypted part of pgp/mime-formatted messages as text/plain.

Tools like Mailvelope https://www.mailvelope.com/ can handle multiparted messages fine, but only if they can get their hands on it.

To customize the text that prefixes the displayed message-part see localization/

Confirmed to be working with Roundcube v1.0.x and v1.1.x.

To use the plugin drop the code into Roundcube's plugins-folder and enable it in Roundcube's config. E.g.:

cd $roundcube/plugins
git clone git://github.com/posteo/show_pgp_mime
vim ../config/config.inc.php

The feature will be enabled for all users if the plugin is activated. You can control the default by setting the following option in Roundcube config:

// display of encrypted pgp/mime content in mail view
$config['show_pgp_mime'] = false;

Any contribution is welcome! Feel free to open an issue or do a pull request at github.com.