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.