Email Robot

i need an email robot script Containing these features : - it Can respond to any email by a certain word .. Example , whene i send " hi " he Will answer " hello" - the robot Able to send attachments " 5MB or more " - the robot must work for any email like gmail or same domain name - i can add many email for that robot "As a sender" - anyone can Subscribe by sending some word like " join " the script has admin page only : - add , edit and confirm emails - add , edite messages robot with attachment of each word i want - page to see all the massge sent the script must support arabic Language .. the script is very simple so I hope cost is not high