Use an encrypted connection in your e-mail software, in compliance with the e-mail service provider's instructions. The encrypted connection between the computer and e-mail server, specified in the communication settings of the e-mail software, will protect the connection from eavesdropping.
Furthermore, the contents of e-mail messages containing confidential information should also be encrypted whenever necessary.
E-mail message contents can be encrypted by using an additional encryption method in addition to the actual e-mail software. In this case, the encryption method used should be agreed on with the message recipient. In most cases, the recipient must use the same encryption software for decrypting the message, and the recipient must know the password used for encryption.
For concealing message contents, you can use software intended for e-mail protection, such as PGP (Pretty Good Privacy), or you can send the contents of the message in a password-protected file as an attachment.
You cannot encrypt the recipient's email address, because it is used for routing the message to the recipient.