How does throttling prevent IP reputation loss?
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Sending too fast is one of the quickest ways to hurt a new IP. Throttling, slowing down how many messages you push out per hour or per connection, keeps you from flooding recipient servers before they've had a chance to build trust in you.
Mailbox providers cap how much mail they'll accept from any single IP in a given window. If you burst past those limits, you'll get 4xx deferrals at best, or outright blocks at worst. A well-throttled send that respects those limits looks nothing like the spray-and-pray approach spammers use. That difference matters to filters.
During IP warming, throttling is especially important. A brand-new IP that suddenly sends 100,000 messages a day will almost certainly land in spam or get blocked. The same IP sending 500 messages a day for a week, then 1,000, then 5,000, tells a completely different story. The gradual ramp signals legitimate, consistent use rather than a one-off blast.
Throttling also protects you after a reputation knock. If your complaint rate spikes or you land on a blocklist, pulling back volume gives your reputation time to recover. Hammering forward at full speed doesn't.
Most ESPs handle throttling automatically based on per-provider rules. If you're running your own MTA, you'll configure connection limits, rate delays, and per-destination concurrency manually. Either way, the principle is the same: send at a pace the receiver can accept, and back off when they push back.
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