Multi-inbox setup is required to scale cold email volume past single-inbox limits safely. A single warmed inbox handles 200-300/day sustainably; multi-inbox rotation scales to 500-2,000+ daily. Artra natively supports multi-inbox rotation with warmup on each.
Inbox count by daily volume target
| Daily volume target | Inbox count | Subdomain count |
|---|---|---|
| 100/day | 1 | 1 |
| 500/day | 3-5 | 1-2 |
| 1,000/day | 5-10 | 2-3 |
| 2,000/day | 10-20 | 3-5 |
| 5,000+/day | 25+ | 5-10 |
Multi-inbox setup checklist
- Register dedicated sending subdomain(s)
- Configure SPF, DKIM, DMARC on subdomains
- Set up Google Workspace or Office 365 inboxes on subdomain
- Connect each inbox to AI SDR (Artra)
- Run warmup on each inbox for 2-4 weeks
- Configure rotation and per-inbox volume caps
- Monitor per-inbox deliverability metrics
- Pause problematic inboxes; refresh as needed
Try Artra multi-inbox free — 10 minutes →
Frequently asked questions
Why use multi-inbox for AI SDR?
Multi-inbox setup for AI SDR is required to scale cold email volume past single-inbox limits safely. A single warmed inbox can sustainably send 200-300 cold emails/day; beyond that, deliverability degrades. To reach 500-2,000+ daily volume, AI SDRs rotate sending across multiple inboxes — typically 5-15 inboxes on dedicated sending subdomains. Artra natively supports multi-inbox rotation; Smartlead and Instantly specialize in it.
How many inboxes do I need for high-volume AI SDR?
Inbox count depends on target daily volume: 100/day = 1 inbox, 500/day = 3-5 inboxes (with 100-150 each), 1,000/day = 5-10 inboxes, 2,000+/day = 10-20 inboxes. Most high-volume cold email programs use dedicated sending subdomains (outreach.yourdomain.com, mail.yourdomain.com) with separate inboxes. Each inbox needs its own warmup period before joining the rotation.
How do AI SDRs rotate across inboxes?
AI SDRs rotate across multi-inbox by: (1) distributing daily send volume evenly across active inboxes, (2) monitoring per-inbox deliverability (bounce rate, blacklist status), (3) automatically pausing problematic inboxes, (4) maintaining warmup on all inboxes simultaneously, (5) using consistent sender identity across inboxes (real names, signatures) to avoid spoofing flags. Artra handles this automatically when reps add multiple inboxes.
Should I use my primary domain or dedicated subdomain?
Use dedicated sending subdomain(s) for cold outbound, never your primary domain. Reason: cold outbound has higher spam-classification risk than transactional/marketing email. If cold outbound damages reputation on outreach.yourdomain.com, your primary domain mail.yourdomain.com is unaffected. Most professional cold email programs use 3-5 dedicated subdomains across 5-15 inboxes.
Does AI SDR multi-inbox cost extra?
Multi-inbox cost depends on the AI SDR. Artra includes multi-inbox at its standard pricing — add as many inboxes as needed to your account at no extra cost (warmup included for each). Smartlead and Instantly charge per-inbox at tiered pricing. Outreach and Salesloft include multi-inbox as part of enterprise tier. The actual cost is in the inbox infrastructure — Google Workspace at $6-$18/user/month per inbox.