PHP mail() works from command line but not apache

I'm trying to figure out why the mail function in PHP fails when called via web browser (i.e. apache), but I can run the same script from the command line using

php -f mailtest.php

This is one of my client's Fedora servers, so I don't grok it completely, but I do have root access should I need to change anything.

from php.ini:

sendmail_path = /usr/sbin/sendmail -t -i

Not sure if this could matter, but /usr/sbin/sendmail is a symlink to /etc/alternatives/mta, which is a symlink back to /usr/sbin/sendmail.sendmail. FWIW the apache user does have permission to run sendmail (tested sendmail directly from the command line).

OS: Fedora Core 7 Linux (kernel 2.6.23.17)  
Apache: 2.2.8  

PHP: 5.2.6

Any help here will be greatly appreciated!

Answer

I found the problem. SELinux was preventing apache from being able to use sendmail. To diagnose, I used

$ sestatus -b | grep sendmail  
httpd_can_sendmail                   off

Then to actually fix the problem:

$ restorecon /usr/sbin/sendmail
$ setsebool -P httpd_can_sendmail 1

Read more about it here.