Scientific Letter is an original mail program that allows you to create messages with complex equations. The equation editor used in the mailer allows you to create complex letters in about the same time as a normal letter would take. Recipients of letters from Scientific Letter who use other mailers will see the message text with equations included in it as a LaTeX notation. "Hot keys" used in the software and pop-up windows allow you to type a complex mathematical text much faster than in LaTeX. Text with simple equations is easily handled. You don't need an index of LaTeX commands. Equations in the message editor are displayed in their natural form.