How can I configure Horde under cPanel to display HTML emails? [closed]

In cPanel, Horde does not display rich text/HTML emails by default, it only displays the plain text version. I know there is an option to display HTML emails, but I am not sure how to enable that under cPanel.

I read a lot of forum posts online saying that I need to set $mime_drivers['html']['inline']=true; in mime_drivers.php. However if I alter this file I am afraid that cPanel will overwrite it. cPanel has a tendency to overwrite files I modify.

How can I configure Horde under cPanel to display HTML emails?

This question had me stumped for a long while. Months ago I was unable to find the answer and so I just edited /usr/local/cpanel/base/horde/imp/config/mime_drivers.php, specifically changing the section:

$mime_drivers['imp']['html'] = array(   
    'inline' => false,

to:

$mime_drivers['imp']['html'] = array(   
    'inline' => true,

As I feared, every time cPanel updated Horde, this change would be lost and my users would complain. Now, I believe I have found a solution. (However Horde has not yet updated so I am unable to tell for sure if this works).

After including imp/config/mime_drivers.php, Horde will check for a directory imp/config/mime_drivers.d/ and, if found, will include() all files ending in .php in that directory. This directory does not exist under cPanel, so it can be created without fear of being overwritten.

The file /usr/local/cpanel/src/3rdparty/gpl/README-horde contains details on how cPanel updates Horde, as well as instructions on customizing Horde. A few relevant excepts of that file give clues as to how to make the customizations I wanted permanently:

During the maintenance phase of /scripts/upcp and /scripts/maintenance, the webmail script found at /usr/local/cpanel/install/webmail is executed. This in turn executes /usr/local/cpanel/bin/update-horde. Presented below is an outline of steps update-horde performs:

1. The Horde installation is wiped clean (rm -rf /usr/local/cpanel/base/horde).
2. Using the version specified in update-horde, the appropriate Horde source tarball will be extracted to /usr/local/cpanel/base.

[...]

After determining which tarball to use for the source install, and extracting it, the update-horde script checks for the following:

    o /var/cpanel/horde/overlay.tar
    o /var/cpanel/horde/overlay.tar.gz
    o /var/cpanel/horde/overlay.$hordever.tar
    o /var/cpanel/horde/overlay.$hordever.tar.gz

As with the prior tarballs, the value of $hordever must match what is defined in the update-horde script. The overlay tarball provides a simple way of customizing specific aspects of Horde. For example, certain graphics, themes, modules, plugins and the like can all be provided as an overlay. Since it is extracted into /usr/local/cpanel/base, the contents of the tarball must match the directory layout found in /usr/local/cpanel/base/horde.

From this file I was able to discover the following steps to override the inline HTML view setting is as follows:

tl;dr: here are the steps:

1. In a temporary directory, create the horde/imp/config/mime_drivers.d/ directory structure which cPanel expects:

   mkdir -p /tmp/horde/imp/config/mime_drivers.d
   

2. Create an override file in that new directory. I named mine html.php but you can name it anything you like as long as it ends in .php

3. Insert the following contents into /tmp/horde/imp/config/mime_drivers.d/html.php:

   <?php
   /**
    * HTML driver settings
    */
   $mime_drivers['imp']['html'] = array(
       'inline' => true,
       'handles' => array(
           'text/html'
       ),
       'icons' => array(
           'default' => 'html.png'
       ),
       /* If you don't want to display the link to open the HTML content in a
        * separate window, set the following to false. */
       'external' => true,
       /* Run 'tidy' on all HTML output? This requires at least version 2.0 of the
        * PECL 'tidy' extension to be installed on your system. */
       'tidy' => false,
       /* Check for phishing exploits? */
       'phishing_check' => true
   );
   

4. Create a .tar.gz version of the /tmp/horde directory at /var/cpanel/horde/overlay.tar.gz:

   cd /tmp
   tar -czvf /var/cpanel/horde/overlay.tar.gz horde
   

   This file should be expanded by cPanel every time Horde is updated, re-adding your configuration override.

5. Move the /tmp/horde/imp/config/mime_drivers.d/ into place:

   mv /tmp/horde/imp/config/mime_drivers.d /usr/local/cpanel/base/horde/imp/config/
   

6. Log in to Horde to test.