Encrypts the message.
async ssmtp.encrypt(): Promise<void>
This method encrypts the input message in a PKCS encoded envelope with all of the recipient certificates specified in the MessageRecipients properties.
Please note that the message headers, including the Sender, Recipient(s), and Subject, are not encrypted. If this is sensitive information, consider including these headers in the message body as a MIME entity, and providing other headers for the S/MIME wrapper.