How to enable php5 at 1and1

With 1&1 Linux hosting packages you have the choice between PHP4, PHP5 and PHP6. 1&1 Web Hosting packages use PHP4 as default for all .php files.
Why 1and1 still using php4 as default? It is too old. A lot of program are not support php4 any more. Just like phpBB 3.
You may choose to simply name the script with the .php5 file extension if there are only a few scripts that require PHP5. If you don’t want to rename all your scripts to .php5, you can add the following into .htaccess file.

AddType x-mapp-php5 .php

Save the text file as .htaccess in the folder where you need to use PHP5 (or upload the file to the correct folder). The settings specified in the .htaccess file are recursive meaning that the settings will apply to the current folder where the file is saved as well as all subfolders.