If it's just their webmail that's non-free, and you can choose your own
operating system for the VPS, I'd say there isn't really a problem so long as
you avoid the webmail and setup a separate email server yourself.
Do you need webmail, or is it enough to have POP3/IMAP access to your
mailboxes and access them through an email client?
Since you're running your software on somebody else's computer, it's
debatable whether the four freedoms really apply, anyway. Your system is
compromised no matter what you do.
