I understand the importance of using "Head Start" for large email sends, and I get the impression that it's not as critical for small sends. I know, for example, that a webinar invite to 20,000 people needs Head Start, but an event "thank you for attending" email to 30 probably doesn't. Does anyone know where the threshold is as to when you definitely need Head Start?
For context, we are occasionally asked to send time-sensitive emails, and we set the expectation with the rest of the marketing team that we need the email finalized in Marketo 12 hours ahead of time. Is there a definitive number where I can say to the team "if we are sending to more than X people, we need to use Head Start?"