I have written a Python script that checks a certain e-mail address and passes new e-mails to an external program.  How can I get this script to execute 24/7, such as turning it into daemon or service in Linux.  Would I also need a loop that never ends in the program, or can it be done by just having the code re executed multiple times?
Use whatever service manager your system offers - for example under Ubuntu use upstart. This will handle all the details for you such as start on boot, restart on crash, etc.
How to make a Python script run like a service or daemon in Linux