Lyris MailEngine - Version 1.0 Lyris MailEngine is a "mailer" (mail transfer agent) that sends or relays email up to 150,000 messages per hour or more, depending on hardware and Internet connection. This performance enables prompt delivery of time-sensitive content, such as opt-in email about a sale or limited-inventory promotion. MailEngine also helps reduce hardware and maintenance costs by replacing multiple machines running lower-performance mailing software.