Not to mention that the security of your letter increases quite nicely when you use thick paper and seal it shut. Yes, with wax. No, it's not super-secure, but

Not to mention that the security of your letter increases quite nicely when you use thick paper and seal it shut. Yes, with wax. No, it's not super-secure, but it stops most casual snooping attempts. Taking off (and reattaching) a seal without breaking it is quite a bit of work if you choose the right wax.