File extensions on OSTicket 1.6 ST are limited to 3 - 4 digits in the stock distribution. But some times you want to change this to allow for slightly longer or slightly smaller file extensions. Such as .gz or .xhtml.
Edit [document root]/include/class.config.php
circa line X locate the following:
$ext = strtolower(preg_replace("/.*.(.{3,4})$/", "$1", $filename));
and change it to
$ext = strtolower(preg_replace("/.*.(.{2,5})$/", "$1", $filename));
This will allow file extensions as small as 2 character and as large as 5.
Alternatively if you dont care how many characters are in the extentsion you could do
$ext = strtolower(preg_replace("/.*.(.+)$/", "$1", $filename));
Which would allow any extension greater than 0 character.