Dropping per-mailbox volume saved a dying campaign

Dropping per-mailbox volume saved a dying campaign

An agency pushed 80 sends/day per mailbox to move volume fast. Opens fell from 41% to 24% over three weeks — they were over-sending fresh-ish mailboxes.

Fix: dropped to 30/day per mailbox, added 4 more mailboxes to keep total volume flat, kept warm-up running underneath.

Before: 5 mailboxes × 80 = 400/day, 24% open.
After: 9 mailboxes × 30 = 270/day, opens recovered to 39% in two weeks, then scaled back up to 400 at 39%.

Pros
— Lower per-seat volume protects reputation
— More mailboxes = resilience
Cons
— More mailboxes = more cost + DNS
— Slower ramp to target volume

Verdict: 4.5/5. Volume-per-mailbox is the dial most people set too high.

Who it's for: anyone watching opens decay at high per-seat volume. Skip if you're already under 40/mailbox/day.