This plugin adds a blue button to the compose screen, next to the identities selection dropdown. By clicking it, a textbox will replace the dropdown, allowing you to enter whatever you want as sender value (it must be a valid "From:" header field value, though).
When replying to an e-mail sent to you through an address not in your identities list, plugin will automatically fire and set "From:" header to the address the original e-mail was sent to.
Execute composer require r3c/custom-from from your RoundCube install
directory and run the install command. See instructions from RoundCube website
for details: https://plugins.roundcube.net/.
Clone repository content to a custom_from directory inside your RoundCube
plugins directory, so that file custom_from.php file can be found at
$ROUNDCUBE_INSTALL_DIRECTORY/plugins/custom_from/custom_from.php.
cd $ROUNDCUBE_INSTALL_DIRECTORY
git clone https://github.com/r3c/custom_from.git
Then reference plugin by adding an item "custom_from" to RoundCube plugins list
in configuration (variable $config['plugins'] variable in file
$ROUNDCUBE_INSTALL_DIRECTORY/config/main.inc.php). Ensure your web user has
read access to the plugin directory and all files in it.
Once plugin is installed, custom sender button will appear at the right
hand side of the identity selection list, with icon 
.
If you want to disable the "automatic replacement on reply" feature, for all users, rename
config.inc.php.dist file into config.inc.php, uncomment the line with a
parameter named custom_from_compose_auto and set this value to false.
On the settings page, in the Preferences menu, Reply settings section, you can see plugin settings individually for each user, you can configure various options for Reply:
- Receiving email address — replies from the receiving email address without adding parameters.
- Receiving email address with matching identity — replies from the receiving email address adding parameters (Bcc, Reply-To) of a matching identity.
- Receiving email address with default identity — replies from the receiving email address adding parameters (Bcc, Reply-To) of the default identity.
- Default identity — replies from the default identity.
By default, the Receiving email address with matching identity option is set
- dwurf (https://github.com/dwurf) for the globals $IMAP and $USER fix
- Peter Dey (https://github.com/peterdey) for the custom header feature
- kermit-the-frog (https://github.com/kermit-the-frog) for various bugfixes