Quiet hours, frequency caps, and not becoming the business people mute

Nobody unsubscribes from the message that annoyed them. They unsubscribe from the fourth one, and they attribute the annoyance to your business rather than to your send schedule. By the time it shows in your numbers, the damage is a year old.

Quiet hours

The widely used standard is 8am to 9pm in the recipient's local time zone. That is a floor, not a target — and the time zone part is where implementations quietly fail.

// The recipient's zone, not your server's. This is the bug everyone ships.
export function withinSendWindow(now: Date, timeZone: string) {
  const hour = Number(
    new Intl.DateTimeFormat("en-US", {
      timeZone,
      hour: "numeric",
      hour12: false,
    }).format(now),
  );
  return hour >= 8 && hour < 21;
}
 
// No zone on file? Derive it from the area code, and default to holding
// the message until a safe hour rather than guessing wrong.

Frequency caps that actually hold

Enforce the cap at the send layer, not in each campaign's logic. Otherwise three well-behaved campaigns combine into one badly-behaved week.

• Marketing: at most 2–4 per month. Most small businesses should be at the low end of that.
• Transactional: as needed — but a reminder, a nudge and a follow-up for one appointment is already three messages. Count them.
• Hard daily cap across everything. One message per person per day, except for genuine two-way conversation.
• Never two campaigns in the same 48 hours. Stagger them, and let the send layer enforce it.

export async function canSend(customerId: string, kind: "marketing" | "transactional") {
  const recent = await messagesSince(customerId, days(30));
 
  if (recent.some((m) => isToday(m.sentAt))) return false;          // daily cap
  if (kind === "transactional") return true;                        // expected sends
 
  const marketing = recent.filter((m) => m.kind === "marketing");
  if (marketing.length >= 4) return false;                          // monthly cap
  if (marketing.some((m) => hoursSince(m.sentAt) < 48)) return false;
 
  return true;
}

Watch the leading indicator

Opt-out rate per send is your early-warning system. A stable low rate means your cadence is fine. A rate that climbs across three consecutive sends means you are over-messaging, and it will keep climbing until you cut back. Treat a rising opt-out rate as an outage, not a statistic.

Track it alongside your revenue numbers so the trade-off is visible in one place — measuring ROI covers the reporting.

The cap is not a compliance chore. It is what keeps the channel worth having in year three.