I upgraded to 3.9 and later installed WP SMTP for the first time. Works for me.
The built in mail() functionality is an alternative that works for me, but that is my hosting provider who set everything up OK…
Contact form 7 (with file upload) is the plug-in I use for the messaging part, and it just works without any smtp plug in.
I just needed to white-list the sending email address from my web-host in Google Apps (Admin console>Google Apps>Settings for Gmail>Advanced Settings) under Spam.
Some thing seem to have changed in 3.9 regarding mail(), breaking all smtp plug-ins, but luckily it is now all built in, and the dependency has shifted from the smtp data you put in toward the configuration of your host. Well, for me anyway 🙂
