What channel are Email and SMS in GA4 — Google's official spec has the answer

Have you ever sent a newsletter campaign, checked GA4 the next morning, and found that none of the traffic landed under the Email channel? Or wondered why your SMS blast got bucketed into Referral instead of SMS? If you ask five marketers what channel Email, SMS, and Mobile Push land in inside GA4, you will get five different guesses. "Probably Referral, or (other)?" is the most common answer. But there is no guesswork involved. GA4 has an official Default Channel Group spec that decides exact...