mail() function and AOL users

I use the following php mail function in an online applicaiton program: mail($email, "application submitted", $message, "From: employment@mycompany.com\r\n"); This function does not always work when I modify $message. I have checked for null values for $message already but this does not seem to be the problem. I am trying to develop some sort of pattern of when this function works and when it does not. The only essential difference between the values I pass in for message is the one that does not always work includes a link. Apparently anyone useing AOL email is particularly vulnerable to this problem. Is it likely that AOL and other mail servers sometimes block any email from a web site if it has a link in the main body? Or should I not be useing mail() in this manner to begin with? -Matt