For cold outreach, we recommend 2–3 mailboxes per domain on every Forge product. Each product also has a maximum number of mailboxes you can create on a single domain.
Product | Recommended | Maximum per domain |
|---|---|---|
Mailforge | 2–3 | 5 |
Infraforge | 2–3 | 10 |
Primeforge (Google Workspace or Microsoft 365) | 2–3 | 5 |
The maximum is a technical limit, not a target. If you reach it, you won't be able to create more mailboxes on that domain and will need to use another one.
All mailboxes on a domain share the same domain reputation. This has three practical effects:
If one mailbox gets flagged, every other mailbox on that domain is affected.
Spreading volume across more domains protects your sending. If one domain is burned, the others keep working.
Fewer mailboxes per domain lets you keep each mailbox at a safe daily volume.
Putting many mailboxes on one domain concentrates your risk in a single place. Using more domains with fewer mailboxes each spreads that risk.
Pre-warmed domains come with 3 mailboxes per domain.
Maximum per domain: 5 mailboxes.
Each mailbox uses one mailbox slot on your account.
Maximum per domain: 10 mailboxes.
Each Infraforge setup uses a dedicated IP. We recommend no more than 40 mailboxes per IP. If you need more, you can purchase additional IPs and distribute your mailboxes across them.
Maximum per domain: 5 mailboxes.
If you try to create more, you'll see an error saying the maximum number of mailboxes per domain has been reached.
A domain can host either Google Workspace or Microsoft 365 mailboxes, not both at the same time.
A fully warmed mailbox should send no more than 30 cold emails per day. Use this as a starting point for planning:
Daily volume | Mailboxes needed | Domains (2–3 mailboxes each) |
|---|---|---|
100 emails/day | 4 | 2 |
300 emails/day | 10 | 4–5 |
600 emails/day | 20 | 7–10 |
1,000 emails/day | 35 | 12–18 |
Need more volume? Add more domains rather than more mailboxes per domain.
Don't put all 30 mailboxes on one domain. Instead:
Use 10–15 domains with 2–3 mailboxes each.
Spread your daily volume evenly across all mailboxes.
Keep a few extra domains warming up so you can replace any that get burned.
When a domain has reached its maximum, you can't create another mailbox on it. You have two options:
Use another domain. Buy a new domain or connect one you already own, then create the mailbox there.
Free up space on the same domain. Delete a mailbox you no longer need. On Primeforge, deletion is scheduled, so the mailbox stays on the domain until the scheduled date.
Mailbox slots: you pay for slots, not for individual mailboxes. You need enough free slots on your account to create a mailbox. The minimum is 10 slots, sold in steps of 5.
Active domains only: you can create mailboxes only on domains with Active status. Domains that are still propagating won't appear in the list.
Warm-up: new mailboxes need at least 2 weeks of warm-up before you start sending cold emails. Warm-up in Warmforge is included with every Salesforge plan.
2–3 mailboxes per domain is the recommended setup on all products.
The maximum differs by product: 5 on Mailforge, 10 on Infraforge and 5 on Primeforge.
The maximum is a limit, not a goal. Staying at 2–3 gives you the best deliverability.
To scale, add more domains, not more mailboxes per domain.
Mixing infrastructure (for example Primeforge for quality plus Mailforge or Infraforge for volume) helps protect your sending if one product has an issue.
Use 2–3 mailboxes per domain, never more than the product maximum, and scale by adding domains. If you're not sure about your setup, contact our support team in live chat.
