I encountered intermittent timeout issues with plugin 0.9.5 and WordPress 4.0.1. I solved it with a modified plugin that allows setting the PHPMailer timeout and timelimit values. Wasn't sure how/where to submit the code update so I just put in in a blog post:
http://www.mcbsys.com/techblog/2015/01/increasing-the-wp-mail-smtp-timeout/