Push or email: which one to send
They are not interchangeable. One is for things that are true right now, the other for things worth reading. Sending the wrong one costs you the channel.
Having push, email and SMS in one place invites a bad habit: sending the same message down all three. It doubles the annoyance without doubling the response, and it burns the only channel that is hard to get back.
The useful split is not “which is cheaper”. It is how long the message stays true.
Push is for right now
A lock-screen notification is read within minutes or not at all. That makes it right for things with a clock on them:
- the reward is one visit away
- there are six left and it is four o’clock
- the shop is open late tonight
It is wrong for anything a person would want to come back to, because there is nothing to come back to. Once it is swiped away it is gone.
Email is for things worth keeping
Email is slower, survives, and can carry more than a sentence. It suits the seasonal menu, the new opening hours, the thing with a picture.
It also tolerates being ignored. An unopened email costs you almost nothing; an unwanted notification costs you the notification permission, and with it every message you would have sent for the next two years.
SMS is the expensive one
Per message, and per unit of goodwill. It has the highest open rate of the three and the lowest tolerance for being wasted, which makes it a poor default and a good last resort — the appointment reminder, the “your order is ready”.
If you take one rule from this: never send a push that would have been fine as an email. The reverse mistake is cheap. That one is not.