[InclinedPlane]

Intercepting email between SMTP servers is a much harder problem than intercepting email to and from the mail client, even if both are unencrypted. The latter requires only that the ISP or the LAN of the user to be compromised. If you ever connect through an insufficiently secured WAP then all of your email could be compromised.

However, using a secure link from the client to the mail server cuts down on the area of vulnerability significantly. Now your personal system needs to be compromised, or the backbone internet links between mail servers used by people who contact you need to be compromised. This is a significantly higher bar. Granted, if you want to maximize email security then public/private key encryption is the way to go, but the simple step of using https between the client and the server is a very significant improvement.