There are a few things which you should know about security an encryption. I believe Wige mentioned PGP which I have never used myself but I think it can be both public key encryption and private key.

Public Key Encryption essentially means that the key used to decipher the encryption is passed over public channels and susceptible to interception. People call it a "man in the middle attack".

Private key means the person decrypting the message is the only one privileged to the key or "password" which is capable of decrypting the message.

There are a lot of very neat password crackers on the internet as well. They can brute force or dictionary crack the password used for decryption by making millions of guesses to determine the correct answer. But besides breaking the encryption I would guess the security weak point is instead vulnerable to a "side channel attack" (maybe a key stroke recorder).

I am not an encryption expert so I reserve the right to use a word slightly incorrectly.

I know that probably wasn't what you were asking... but nothing is 100% secure... and these terms are probably some of the best to do searches on... just my opinion.

You could always translate your email message to Morse Code?

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James Weisbrod - programmer