I have a simple counter. A personal smtp server, set to listen some non-standard port, set up to do TLS. The mail isn't encrypted, and your boss can still say

I have a simple counter. A personal smtp server, set to listen some non-standard port, set up to do TLS. The mail isn't encrypted, and your boss can still say that you sent mails if he dig up a bit, but he won't spy the content of the e-mails anyway. Just don't make the mistake I did: forget to set up your imap server to use TLS as well.