Introduction
A cPanel accounts tmp/horde/ folder may have large amounts of space used and is due to stale img files. These can be removed periodically without issues.
Procedure
In that cPanel accounts cron job interface you can add the following.
find /home/cpuser/tmp/horde -type f -name 'img*' ! -mtime -2 -exec rm -f {} \;
Be sure the path has the correct path to the users home directory and replace cpuser with the actual cPanel user. This will clear those img files and only leave behind 2 days of files that start with img.