Under some circumstances, a page request can result in nothing more than a blank page. In most cases, this happens after the installation of a plugin, but it can happen elsewhere as well. This problem is typically caused by fatal PHP errors that are simply not being shown on screen.

You can find those errors by looking in your web server log file. The location of that file will be different on some machines, but one example is /var/log/httpd/error_log.

Alternatively, you can tell PHP to display the errors on screen in one of a few ways described below (remember to turn them off again if you are doing this in a production environment):

Change the error reporting settings in php.ini (remember to restart the web server after you make changes to php.ini):

display_errors=On

error_reporting=E_ALL

Change the error reporting settings just for SquirrelMail by adding the following lines into an .htaccess file in the main SquirrelMail directory (this is an Apache web server feature that also requires that you have at least "AllowOverride Options" in the <Directory> section that applies to your SquirrelMail installation within the Apache configuration file).

php_flag display_errors On

php_value error_reporting E_ALL

Install the SquirrelMail Debugger plugin

Note that if you still have trouble seeing errors on screen, make sure you have not overridden the error reporting settings in your Apache configuration file or in another .htaccess file or custom SquirrelMail plugin, etc.

Some more common causes of blank pages are:

You installed a new plugin but forgot to install one of its dependencies (such as the Compatibility plugin) or apply a required patch. Please carefully consult all the documentation files that came with your new plugin, including its README and INSTALL files.

You are attempting to view a folder with a very large number of messages in it (perhaps as many as 10,000). In this case, you may hit the maximum PHP execution time limit or maximum memory limit.

You have installed SquirrelMail for the first time and it does not work at all - even the configuration test page and the login page come up blank. This can be caused by the lack of session support in PHP (which SquirrelMail requires). See the PHP session extension installation manual.