Edit php.ini and search for “mail.log”, check whether this option is enabled or not, if not uncomment it and specify log file name.
# nano /usr/local/lib/php.ini mail.log = /var/log/phpmail.log
# touch /var/log/phpmail.log
File must be writable or owned by apache user.
# chmod 666 /var/log/phpmail.log # chown apache.apache /var/log/phpmail.log
# service httpd restart
# tail -f /var/log/phpmail.log