Limits

Apple doesn’t publish iMessage rate limits, but the signals their spam detection watches are well understood. Messages.dev is built around inbound-first conversations because that’s the pattern that stays comfortably under those signals. The numbers below are the safe operating points we recommend per line.

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Per-line limits

A conversation is inbound-initiated when the recipient texted your line first. Replies inside 24 hours of their last message are effectively unconstrained. Once the 24-hour window lapses, follow-ups count against the 200 / day reach-out budget.

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Signals Apple watches

Treat the table above as the safe envelope for these levers. Drift on any of them and the ceilings effectively shrink:

• Send-to-receive ratio. A line that mostly talks and rarely listens looks like a spammer. Keep it within roughly 10:1.
• Unanswered messages to a single contact. Stop after about 5 messages with no reply on the same thread.
• Daily volume. Volume itself isn’t the problem; volume combined with low recipient diversity or a poor reply ratio is.
• Recipient diversity. Lots of brand-new recipients in a short window reads as a blast.
• Spam reports. A handful of “Report Junk” taps on a single line can trigger restrictions within hours, with no appeals process.

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What happens when you hit a limit

There are two failure modes, and they look different:

1. Messages.dev API limit (1,000 req / hour per key). You get a rate_limit_error with a Retry-After header. Back off until that many seconds have passed.
2. Apple-side throttling. Silent. Sends start slowing down, getting delayed, or stop delivering altogether. There’s no error code and no appeal — the only fix is to back off, fix the upstream pattern (ratio, unanswered messages, daily volume), and let the line cool down.

If a line is consistently flirting with the per-line numbers, the answer isn’t to push harder on that line. It’s to scale horizontally across more lines.

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Warming up a new line

A brand-new line has no history with Apple, and its first ~2 weeks are when it’s most likely to get flagged. Ramp gradually: low volume the first few days, increase as the line accumulates real two-way conversations, and expect to operate well under the per-line numbers above until the line is established. Don’t assume a fresh line can immediately match an older line’s volume.

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