A web server I manage is having problems sending mail from PHP. This server uses exim4 for MTA, and it is configured correctly.
I can send emails from PHP's CLI, but not from the web. i.e. if I do "php mailtest.php" on the command line, the email gets sent correctly, but if I browse to server.com/mailtest.php, mail() returns false and the email never gets sent. Nothing appears in the exim mainlog.
Any advice, or things I should look for ?