Very few Web e-mail providers offer POP service through OE or similar clients. Some offer them at a cost. But I doubt that any secure e-mail provider would allow you to get e-mail through OE, because then you lose the secure connection.
With PGP or similar encryption through your ISP e-mail, your messages are completely secure from the minute you finish typing it and send it to the minute your recipient opens it (assuming the recipient is also using PGP). You'll hear rumors that PGP contains a government backdoor, but many experts have read the source, and there's no backdoor. Invalid Link Removed an explanation from PGP's creator, Phil Zimmerman.