February 18, 2026
SMTP Rotation: Why and How to Set Up Multi-Inbox Sending
Learn why SMTP rotation improves cold email deliverability and how to set up multi-inbox sending. Step-by-step guide with provider recommendations.
What is SMTP rotation?
SMTP rotation means sending your cold emails through multiple mailboxes instead of just one. Instead of sending 100 emails from one inbox, you send 33 from inbox A, 33 from inbox B, and 34 from inbox C.
Why rotation matters
Email providers track sending volume per mailbox. High volume from a single mailbox triggers spam filters. Rotation solves this:
| Metric | Single mailbox | 3 mailboxes rotated |
|---|---|---|
| Daily volume | 50 safe max | 150 safe total |
| Risk per mailbox | High | Low |
| If one gets throttled | All sends stop | 2 others continue |
| Warm-up time | 4 weeks to 50/day | 4 weeks to 150/day |
| Provider diversity | None | Can mix Gmail + Outlook |
How to set up multi-inbox rotation
Step 1: Create multiple sending domains
- yourbrand-mail.com
- getyourbrand.com
- yourbrandhq.com
Cost: ~$10-15 per domain per year.
Step 2: Set up mailboxes on each domain
- sarah@yourbrand-mail.com
- sarah@getyourbrand.com
- sarah@yourbrandhq.com
Step 3: Configure DNS for each domain
- SPF record
- DKIM signature
- DMARC policy
Test each with mail-tester.com — all must score 9+/10.
Step 4: Warm up each mailbox
- Week 1: 5-10 emails/day
- Week 2: 10-20 emails/day
- Week 3: 20-40 emails/day
- Week 4: 40-50 emails/day
Step 5: Connect all mailboxes to your tool
In HeraMail, go to Settings → SMTP and add each mailbox. When you dispatch a campaign, HeraMail automatically rotates through your connected mailboxes using round-robin distribution.
Provider recommendations
| Provider | Price | Sending limit | Best for |
|---|---|---|---|
| Google Workspace | $6/user/mo | 2,000/day | Reliability |
| Microsoft 365 | $6/user/mo | 10,000/day | Volume |
| Zoho Mail | $1/user/mo | 250/day | Budget |
| OVH | $2/mailbox/mo | 200/day | Europe/GDPR |
| Amazon SES | Pay per email | 50,000/day | High volume |
Best practices
- Diversify providers — Don't put all mailboxes on Gmail. Mix providers.
- Match sender names — Use the same person's name across mailboxes for consistency
- Keep volume below 50/mailbox/day — Even with rotation, stay conservative
- Monitor each mailbox separately — Check bounce rates per inbox
- Rotate, don't blast — Spread sends throughout the day
Rotation checklist
- [ ] 2-3 separate sending domains purchased
- [ ] SPF, DKIM, DMARC configured on each domain
- [ ] Mailboxes created on each domain
- [ ] Each mailbox warmed up for 2+ weeks
- [ ] All mailboxes connected to your cold email tool
- [ ] Daily volume stays below 50 per mailbox
- [ ] Bounce rate monitored per mailbox
HeraMail supports multi-SMTP rotation natively — add your mailboxes and we handle the round-robin: heramail.io