In terms of ownership of data, Fastmail is definitely not ideal. However, I trust a company that has a single paid product and employees committed to the point

In terms of ownership of data, Fastmail is definitely not ideal. However, I trust a company that has a single paid product and employees committed to the point of buying the company back from their acquirer (http://blog.fastmail.com/2013/09/25/exciting-news-fastmail-staff-purchase-the-business-from-opera/ http://blog.fastmail.com/2013/09/25/exciting-news-fastmail-s...) more than a company with a free product committed to monetizing me and my data. I recently switched from a setup similar to yours (Postfix+Dovecot+sup) to Fastmail because I'll never have to worry about deliverability again and Fastmail's web client is miles beyond anything else other there, especially the open source offerings (Mailpile looks promising though! I'm hoping this won't stay the case).