Why must I issue a HTTPD -K stop and HTTPD -K start to get PHP Mail to function?

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http://stackoverflow.com – Running a Fedora 15 LAMP. Created a PHP script to send an email. At first go, the email would not appear in any inbox or spam - trying multiple addresses. I attempted to restart PHP by - HTTPD -K restart. -No Joy - But when I restart like this... HTTPD -K stop HTTPD -K start Bam! Email works. I shutdown the server and can replicate the results. So why do I need to do this - I assuming I some type of service startup sequence thing going on? Ideas? (HowTos)