Just a point about Encryption. It's dependent on if you are using already created algorithms or one you've tailor-made. If you've made it yourself you are likely to draw attention if the
powers that be find any investigation impeded by your cryptology prowess. (I know that some countries might ask for your key to decrypting, while others are actually allowed to install spyware on your computer to take the key from you without necessarily informing you.)
Obviously as people have mentioned if you have secure data you want to keep that way then your best encrypting it through PGP. (I'd suggest that any company sending internal Memos/Emails uses this method to lessen Industrial Espionage, usually such emails also have a added disclaimer in the template to suggest that it should not be sent unencrypted or received unencrypted.)
As for reading Emails, well we can use the old
Alice & Bob analogy.
Alice sends Bob an Email. The email is sent directly from Alices Computer to the Mailserver that the Domain Record for Bob's domain points to. On delivery it sits waiting for Bob to either download via POP3, Access via a Website or connect to via the IMAP protocol. The only time this email is truly secure is when Bob has received it and removed it from the server.
This means that for their to be any faults in the
chain in regards to securing this transaction, then their is a chance for exploitation.
For instance if Alice or Bob were to receive a virus from Marvin who's previously setup his own Server as a Proxy, then it's possible for him to point Bob or Alice's software into believing that it needs to use the Proxy to connect to the internet. If this is the case then Marvin can manipulate all outbound connections perhaps he could make it disappear into his own server, perhaps he'd just transparently packet scan the information passing through. (The reason Marvin would pick Alice and Bob is because it's likely that Alice/Bob are Casual Computer users that are likely not to pick up on exploits or know how to tighten their security settings. They are a Soft target in comparison to the Email server, which will have communication logs and require a whole lot of work setting up
Long tracible routes. [This means it takes a long time to trace])
This is of course where Cryptology comes into play, because then even if Marvin manages to intercept the Email he's still got the task of dealing with it in an encrypted format.
