We'll detail everything you need to know about how to invite a guest speaker, from the earliest planning stages to drafting a formal speaker invitation letter. We are excited to invite you to join us as a featured speaker at this event.Your invitation should be a formal email (or letter). Outline the reasons why you've chosen them as the best person to speak at your event. For invitations to events, I always advise that one should send out 6 weeks in advance to the date of the event. A recipient must respond within one week. Letter in the Appendix. On or about June 2, 2019, SUN directed CC1 to pick up the invitation letter at her parents' house in the Eastern District of New York. This guide is an invitation to dialogue.