Three reminders is the standard. Three weeks in advance: a preview of the program’s content (goal: to spark curiosity). One week in advance: practical details on the venue, parking, and dress code (goal: to lower the barrier to entry). The day before: a brief, personal message (goal: to encourage attendance).
More than three quickly starts to feel like spam. Fewer than three is a missed opportunity. Participants view three reminders as a service, not as a nuisance.