Glossary entry
Mailbox rotation
Also known as Inbox rotation · Domain pooling
The practice of rotating sends across multiple email mailboxes (and sometimes domains) to stay under per-mailbox volume thresholds that hurt deliverability. The infrastructure layer modern cold-email operators care about most. Best practice: ≤40 sends/day per mailbox, ≤200 per sending domain, rotate across 3-8 mailboxes per SDR. Tools: Instantly, Smartlead, Mailshake. Critical to pair with email warmup.
01Definition
TLDR
The practice of rotating sends across multiple email mailboxes (and sometimes domains) to stay under per-mailbox volume thresholds that hurt deliverability. The infrastructure layer modern cold-email operators care about most. Best practice: ≤40 sends/day per mailbox, ≤200 per sending domain, rotate across 3-8 mailboxes per SDR. Tools: Instantly, Smartlead, Mailshake. Critical to pair with email warmup.
02Why it matters
The technical detail that determines whether your campaign lands in inbox or spam at scale. Underestimated by non-deliverability-aware teams.
03Example
Worked example
SDR sending 200/day → uses 6 mailboxes at 33-40 sends each, rotates across 2 sending domains.
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