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. Discover considerations, best practices, and essential elements of a wellstructured speaker invitation letter.1 Formatting the Letter. Format the invitation as you would a formal business letter. To provide the QUICKEST turnaround for this, please fill in the form below and we should be able to get back to you within 48 hours. I am writing this letter to inform you about the upcoming__( mention the occasion or the event) It has been a while since we all have met up. Thank you for contacting SAMHSA's External Engagement Team. We appreciate your interest in inviting SAMHSA to participate in your event. Please attach your paper (complete or ERF) or doctoral consortium acceptance letter, if applicable. (Download and fill out these documents).