How many inboxes do you actually need?
Plug in your campaign. Get the exact infrastructure, warmup runway, and expected outcomes — built on real benchmarks.
How many people in your outreach list?
Most multi-touch sequences run 5–7 touches.
10 actual sending days (weekdays only).
Recommended — weekend sends have lower open rates and look spammy.
Used to back-calculate when to start warming inboxes.
Infrastructure assumptions (advanced)
30 is the safe limit. 50+ burns deliverability fast.
3 is the sweet spot. More = spam signal.
New inboxes need warmup before real sends. 3 weeks is standard.
Allston Labs spins up the domains, warms the inboxes, writes the sequences, and runs the campaign end-to-end. Forward-deployed engineering for GTM.
Partner with us →Don't want to build this yourself?
Allston Labs spins up the domains, warms the inboxes, writes the sequences, and runs the campaign end-to-end. We live in your Slack — you stay focused on closing.
Every number comes from a hard constraint.
Email deliverability rules dictate the math. Push past them and you burn the domain.
Above 30 sends per inbox per day, providers start flagging you. 50+ and you burn the domain inside a week. This is the single hardest cap in cold email.
Each domain can host 2–3 sending inboxes before pattern-matching marks it as bulk. The fix isn't more inboxes — it's more domains.
A fresh inbox can't send 30/day on day one. You drip-warm for 2–3 weeks (1 → 5 → 15 → 30) so reputation accrues before real outreach starts.
Weekend sends have ~40% lower open rates and are a strong spam signal. Plan around ~20 sending days a month, not 30.
Single-touch campaigns reply at <0.5%. The reply curve doesn't really start until touch 3, and most of the volume comes from touches 4–7.
Above 3% bounces, providers route your domain straight to spam. List quality matters more than volume — verify before you send.
Learn the craft.
The complete cold email infrastructure reference
Every authentication protocol, every monitoring stream, every operational discipline a B2B sender has to internalize in 2026. SPF, DKIM, DMARC, MTA-STS, BIMI, ARC, subdomain isolation, warmup, bulk-sender compliance, Postmaster, bounce taxonomy, seed-list testing, reply detection — 14 RFC-grounded chapters.
How many inboxes do I need for cold email?
The complete back-of-envelope formula plus worked examples for 250, 1k, 2.5k, and 5k contact lists.
Built for founders who'd rather close pipeline than babysit inboxes.
We embed in your Slack, register and warm the domains, write the multi-touch sequences, and route every reply straight back to your sales team. Forward-deployed engineering for GTM.