Phishing poses a significant threat to the future of commercial e-mail, online banking and online commerce. There is a simple, straightforward and easy-to-use technique that many businesses could start using today. The S/MIME system for sending secure e-mails was developed by RSA Security in the 1990s and adopted as an Internet standard by the Internet Engineering Task Force in 1998. People don’t need a certificate to receive a message that’s digitally signed but not encrypted, that’s because it’s the sender of a digitally signed message who needs the certificate.”]
Source: https://www.csoonline.com/article/2120485/secure-email-via-s-mime.html