As Ultra pointed out, cron is really the wrong tool for this sort of task -- put all thoughts of cron out of your mind. And as CountZero pointed out, you don't seem to have any reason to make this so complicated.

If you have message content in a text file, and a list of email addresses in another file, simply launch some kind of script (perl or shell) that will mail the text to the address list. (Or maybe there's some function or facility in PHP that handles this?)

If you think it really can't be as simple as that, we can't give you any better answer yet, because you haven't told us what the complicating factors are.