I would recommend not using Linode and realize your e-mail will be terribly unreliable if you run your own e-mail server (even if you setup DKIM, SPF and DMARC. Google/Microsoft don't give a shit about any of that). I wrote a post about this a while back:

http://penguindreams.org/blog/how-google-and-microsoft-made-...

I've considered moving to Vultr since they block SMTP/25 by default and individual customers have to get it enabled (which seems like it should reduce false positive spam classification as more e-mail providers).