"cubic" is a key word here.
Good point. 5x5 still works for me.
Plus there's no expectation that FedEx would (or should) have access to the *contents* of your mail, but an ISP-hosted email account, currently, does have full access to the content, with your tacit approval.
Hmm. Have you worked at Fedex or UPS? You wouldn't believe the condition that those packages end up in and in many cases the contents are exposed and the package handlers are required to re-seal them.
* POP email with "delete from server" active will limit how much of your mail your ISP has access to.
Seriously? What guarantee do you have that "delete from server" is a true deletion rather than an archive function? What about backups? What about cleaning up of the residual message from the slack space?
* Run your own mailserver.
Your message must still travel through other data networks and mail servers to reach it's destination. Through every leg of the route there is opportunity for the message to be captured via network traces. Through every mail server that the message passes through the message, at least briefly, lands in the mail servers message que until it is forwarded on; not to mention the log messages that may also be generated. What guarantee do you have that the mail server isn't configured to forward a copy of all messages to some unscrupulous individual?
* Develop a mailserver that stores mail in an encrypted folder and requires your key to access.
A little better but that would only account for the message after it as arrived in your encrypted folder. To truly secure the message, it must be encrypted prior to transmission and the only person that should be able to decrypt the message should be the intended recipient.
"...you ask the IT department (dad)."
"The eleventh commandment was `Thou Shalt Compute' or `Thou Shalt Not Compute' -- I forget which." -- Epigrams in Programming, ACM SIGPLAN Sept. 1982