Bounce and complaint thresholds
Defrost automatically pauses any campaign whose bounce rate crosses 3% — tightened from the 5% industry rule of thumb, because reputation damage from bounces is not linear and waiting for 5% lets real damage accumulate first.
Before that hard pause, a campaign is throttled to half its normal send rate the moment its bounce rate crosses 2%, and gets an early warning at 1.5% so a human can look before either automatic response fires.
Complaint (spam-report) rate has its own, stricter ladder: an early warning at 0.05% and a hard auto-pause at 0.1% — tightened from an earlier 0.3% threshold to match mailbox providers’ 2024 bulk-sender complaint limits.
Both auto-pause gates wait for a minimum sample before they can fire: at least 50 sends for the bounce-rate gate and at least 20 sends for the complaint-rate gate, so a single early bounce or complaint on a tiny send window can’t trip a false pause on an otherwise healthy campaign.
Send-rate and volume caps
A fully warmed mailbox is capped at 50 emails per day, enforced at send time on every account regardless of plan tier.
A mailbox still in its warmup period is capped at 20 emails per day of real prospect sending, and follows a 30-day volume ramp underneath that ceiling: 5 emails per day for days 1-5, 10 for days 6-10, 20 for days 11-15, 35 for days 16-20, and 50 for days 21-30.
Every send is spaced 30 to 60 seconds apart from the one before it, a randomized delay window enforced on every campaign to keep sending patterns from looking automated to mailbox providers.
Sends to any single receiving domain (Gmail, Outlook, and the like) are capped at 30 per hour and 200 per day per sending organization, independent of how many mailboxes that organization is sending from, so no single inbox provider ever sees a volume spike from one sender.
Verification and lead quotas
Every lead is checked against a minimum valid-email-rate floor before a campaign is allowed to proceed: 85% when multi-provider email verification is active, or 50% in the degraded mode where verification providers are unavailable and pattern-based discovery is the only signal.
Each mailbox is budgeted for 250 leads per month — derived from a real 25-cold-sends-per-day discipline (half of a fully warmed mailbox’s 50/day ceiling, with the other half reserved for ongoing warmup) at roughly two effective touches per lead. A plan’s total monthly lead quota is its mailbox count multiplied by this same 250-per-mailbox figure.
Reputation-adaptive warmup
Warmup volume isn’t just a fixed ramp — it adjusts to real delivery signal. Over a rolling 7-day window, a bounce rate above 2% cuts that mailbox’s daily volume to 75%, a bounce rate above 4% cuts it further to 50%, and a bounce rate above 5% pauses warmup sends for 24 hours.
The same rolling window watches for silent inbox filtering that never shows up as a bounce: if fewer than 10% of a mailbox’s sends are actually delivered, warmup pauses outright, and delivery under 50% halves the daily volume.
Warmup can also accelerate: a reply rate above 30% combined with a bounce rate under 1% increases daily volume by 20%, capped at no more than 20 additional sends per day above the scheduled ramp figure.
A mailbox that sustains a 3-day bounce rate above 3%, or a 7-day bounce rate above 5%, is demoted from “warm” back to “warming” status and rolled back to day 11 of the 30-day ramp (the 20-email-per-day tier) rather than starting over from zero.
Shared-infrastructure fences
On Defrost’s managed sending relay, a single organization’s cold sends are capped at 500 per billing cycle by default, rising to 20,000 per cycle for Agency-tier organizations — a deliberate fence so one high-volume tenant can never exhaust shared sending capacity or degrade delivery for every other organization on the same relay.