Email content is encrypted, indeed, it protects email contents from any way of stealing in the transmitting process. However, SSL certificate deployed on mail server protects your password for log into your email account. If the mail server is not deployed with a SSL certificate, your password will be transmitted to the server in plain text. Illegal person can steal the password to login your email and then get your email certificate and may be able to decrypt your encrypted emails.
If you have known that your email provider does not have SSL deployed on the mail server, we suggest you use service from another provider. If it is your own mail server, please apply for an SSL certificate for it as soon as possible.