Why secure your email? Well, because you can? The traditional protocols for email transmission are SMTP and PO3 (as well as IMAP). None of these protocols are natively secure. There are advanced versions of the protocols, and they could be "wrapped" in secure transfer protocols. Most email providers traditionally did not bother to provide the secure versions of the protocols, and even when the email clients support the secure versions, users often did not know how or take the time to use those secure options.
With the proliferation of online, Web-based email services, every major ISP and many other companies offered Web based email. These mail services again often did not offer any security options, or if they did, only offered simple security measures such as SSL via HTTPS for the connection to their servers. There is far more to email security than this.
Let's take a look at three of the top free truly secure email services. Try them and see which one suits your needs and makes the most sense. Maybe not every email you send needs to be secured, but when an email does need to be, one of these services will meet that need.