WordPress 3.3.2 and CF7 version 3.1.2.
What resolved the issue for me was to change the “to address” of the form to an email address not on the same shared server. I was originally using a “to address” from an email account of a different domain with an MX record on the same shared server (I have several sites on the same server). I changed the “to address” to a [email protected] address and that solved the problem for me. Maybe this will help some of you. Fortunately, (in my case) the project called for sending to a gmail address anyway. It was my testing email address that was problematic.