Scott Kingsley Clark on "[Plugin: WP Mail SMTP] SMTPAutoTLS overrides SMTPSecure (no-TLS/SSL) in PHP 5.6+"

In PHP 5.6+, if you are using this plugin and have no TLS or SSL enabled, it will automatically use TLS.

Currently, the code in the plugin does this:

$phpmailer->SMTPSecure = get_option('smtp_ssl') == 'none' ? '' : get_option('smtp_ssl');

But what it needs is another few lines below that:

if ( empty( $phpmailer->SMTPSecure ) ) {
    $phpmailer->SMTPAutoTLS = false;
}

Not vouching for the decision to use no security here, but just posting this in the hopes that @chmac sees it and this makes for a quick and easy fix in his next release.

https://wordpress.org/plugins/wp-mail-smtp/