The primary objective of email encryption is to make sure your email messages stay confidential. Encryption prevents anyone other than the desired recipient from reading your email’s content.

In order to achieve this goal, encryption transforms the content in your email to garbled text. It looks like long strings of random characters. The encryption process is similar to sealing something in an envelope or locking it in a safe.

The analogy goes further. Content is encrypted with a key, which is a long string of random characters that is technically similar to a standard password. However, the key is more random and way longer.

The reverse process is called decryption. Its objective is to convert the garbled text into a readable form. Just like the analogy given for encryption, decryption is opening the sealed envelope or locking the safe. It also requires a key. The two most commonly used encryption techniques are Symmeric Key Encryption and Public Key Encryption.

As mentioned earlier, a key is needed to seal a message or open it. Once the message is sealed, no one can read the content of the email without a key. The key characteristic of symmetric-key encryption is that both the recipient and sender have the exactly same key. They need to share this key with one another, which is difficult to do in practice. If the sender and recipient exchange the key in E-mail, then the key can be intercepted as well as the sealed message and used for decryption, which defeats the purpose why the E-mail was encrypted in the first place. That leaves the sender and recipient in a quandry - how to exchange keys in such a way that no one get's them in transit? Well, that's where the Public Key Encryption comes to rescue.

Public key encryption involves two different keys - a private key and a public key. Using the safe analogy, the sender of the message uses the public key of the recipient to put messages in the recipient’s safe. This key can not be used to take items out of the safe. It is good only for putting in. In other words, the safe only has a one-way opening.

In order to read a particular message, the recipient needs to use his private key. It is called private because only the intended message recipient has it. The private key allows the recipient to open and access the safe, and read the messages ((or take the message out of the sealed envelope in our analogy). With public-key encryption, there is no need to exchange keys as it was the case with symmetrical key encryption. The recipient generates the private and public keys and publishes the public key so that anyone can use it to encrypt messages to him or her. No one other than the recipient will be able to open these E-mails, since only him or her has the public key, which can be used to open messages.