"How many domains" isn't really the right first question — it's downstream of a simpler one: how many emails per day does this client's campaign actually need to send, and what's the safe volume per inbox.
Safe sending volume per inbox is generally 30–50 emails per day — pushing meaningfully past that threshold risks triggering spam filters and damaging sender reputation, an outcome that's much more expensive to fix than the extra domains cost to prevent. A common baseline configuration is 2–3 mailboxes per domain, which distributes sending patterns and provides backup capacity if one mailbox has an issue. Our own live agency guide recommends 3-5 sending domains per client as a starting baseline, which lines up with the volume math below once you work through a typical client's target send count.
| Target daily volume | Domains needed | Inboxes needed |
|---|---|---|
| ~300 emails/day | 2–3 domains | 6–9 inboxes |
| 1,000+ emails/day | 7–12 domains | 20–35 inboxes |
In monthly terms, 300/day is roughly 6,000–9,000 sends per month per client; 1,000+/day scales to 20,000–30,000+ monthly. Most single-client campaigns in a cold email agency's typical range sit closer to the 300/day tier — the higher tier is more common for larger accounts or agencies running aggressive multi-sequence volume for one client.
Every client needs completely isolated domains and mailboxes — never shared with another client, even briefly. This isn't a cost-optimization opportunity. A deliverability problem on one client's infrastructure — a spike in spam complaints, a blocklist hit — should never be able to affect another client's sender reputation, and shared infrastructure is exactly the failure mode that makes that possible.
See our white-label guide for how sub-account isolation on the platform side reinforces this at the software layer, on top of the domain/mailbox isolation described here.
Use variations of the client's own brand that read as professional, not spammy — for a company called "Acme Corp," reasonable sending-domain variants might be acmecorp.co, getacme.com, or acmegrowth.com. Every sending domain should carry a simple, real landing page; a domain with no content at all is itself a signal to spam filters and to any recipient who checks it out of curiosity.
It depends on target volume — roughly 2-3 domains for a client sending around 300 emails/day, scaling to 7-12 domains for a client sending 1,000+ emails/day. A common baseline recommendation is 3-5 domains per client to start.
Generally 30-50 emails per day per inbox. Pushing meaningfully past that threshold risks triggering spam filters and damaging sender reputation.
No. Every client should have completely isolated domains and mailboxes, never shared with another client — a deliverability problem on one client's infrastructure should never be able to affect another client's sender reputation.
A common baseline is 2-3 mailboxes per domain, which distributes sending patterns and provides backup capacity if one mailbox develops an issue.
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Written by
Scott Holmes
AI systems consultant based in Barrie, Ontario. Founder of Pinnacle Tech Projects. Has built and scaled multi-domain sending infrastructure for cold email agency clients.
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