These four formats reach a person rather than waiting for them to show up. That makes them the most useful and the easiest to overuse.
Appears in the messenger inside your product, as if a teammate wrote it. The gentlest of the four — nothing arrives anywhere, and the customer sees it when they're already with you.
It also invites a reply, which the others don't. That's a feature when you want the conversation, and something to plan for: a proactive message to ten thousand people produces real conversations somebody has to answer.
The only format that reliably reaches someone who has stopped using your product, which makes it the one for expiring trials, failed payments and anything requiring action.
It's also the one with the most rules attached. Send from a verified domain, keep the unsubscribe placeholder in your template, and remember that a marketing message and a service notification are treated differently — by regulators and by spam filters.
Interrupts a phone, which is a lot to ask. Reserve it for things that are genuinely time-sensitive to the person receiving them, not to you.
Reaches people where they already are, with the highest read rate of the four — and the strictest rules. Starting a conversation with someone who hasn't recently written to you requires an approved template, so plan the template before planning the campaign.
It's also the most personal channel on this list. A message that would be unremarkable by email can feel intrusive on WhatsApp, so it suits things the customer is waiting for rather than things you'd like them to know.
Start from where the message has to land. If it only matters while someone is using your product, use a chat message. If it matters when they aren't, use email. Use push and WhatsApp when it's time-critical, and be able to say why.
Sending the same thing on several channels rarely doubles the reach. It mostly doubles the annoyance for the people who got both.
