Check the error log
There may be an error in the script preventing the mail from being sent. In the folder with the script, look for the file error_log. Any errors produced by the script will be recorded there. Learn More.
Sending limitations
The PHP mail() function is limited to 250 emails per day. Once you've reached this limit, the email generated by your scripts will not be sent until the limit resets for the next day. These emails will not be held for delivery, so you may need to recreate and re-send any emails which were not sent if your script reached the 250-per-day email limit.
Learn how to set up PHP mail.
See Also:
