What is the primary function of encryption in emails?

Encryption in emails serves the vital purpose of protecting the content during transmission. This means that when an email is sent, the information it contains is transformed into a code that can only be deciphered by the intended recipient. This security measure ensures that even if an email is intercepted or accessed by unauthorized individuals, the content remains confidential and unreadable without the appropriate decryption key.

The other options do not reflect the primary purpose of encryption. Increasing the size of the email or allowing for faster sending do not relate to the security features encryption provides. Similarly, making messages easy to read contradicts the essence of encryption, since it is designed to obscure the content from anyone who does not have the proper access rights.