The problem with contact form 7 is because of multiple lines in the header (From: + Reply-To:), and the regexp in WP-SES plugin doesn’t support this. But this can easily be fixed by modifying the regexp in wp-ses.php to:
preg_match('/^Reply-To: ([a-z0-9._%+-]+@[a-z0-9.-]+\.[a-z]{2,4})\b/imsU', $headers, $rto)
Notice the /imsU instead of only /i. Meaning that the regexp will be able to find the Reply-To email if $headers contains multiple lines.
As a sidenote, gmail will refuse to use the Reply-To header if a reverse DNS-lookup on the sending email doesn’t match the domain of that email (forgery detection).
