There is a bug in the WordPress 3.6 release that causes Contact-7 forms to fail to be emailed – but it only affects those hosts using Qmail based email systems.
It appears that WordPress used a few month old version of class-phpmailer.php, one where a bug had been introduced for Qmail based email systems. The authors of phpmailer.php had already issued an update for the file, but WordPress issued the 3.6 upgrade with the older class-phpmailer.php version 3.5.4 (version 3.5.5 had already been fixed).
In any event the WordPress core developers are now aware of the issue and have already indicated that a more current version of class-phpmailer.php (one that is fixed for Qmail) will be included when WordPress 3.7 is released.
Meanwhile to correct the issue with the Qmail bug:
- Go to this link- https://github.com/PHPMailer/PHPMailer/blob/master/class.phpmailer.php
- Copy the actual file contents starting with:
- Then replace the contents of your wp-includes/class-phpmailer.php with the code from the above file – that should correct the issue if related to the Qmail bug.
NOTICE!!! the name of the file is class(dash)phpmailer.php, not (dot) as it appears in the second line comment of the source.
Source – http://wordpress.org/support/topic/wp-36-doesnt-work-with-cf7. Thanks to Jack Armstrong for this information.
If you are experiencing problems sending emails, you might consider contacting your hosting provider to ask if they use a Qmail based email system.