Bulk Email Infrastructure: Dedicated IPs and Pools
Build reliable bulk email infrastructure with dedicated IPs, IP pools, warm-up schedules, and traffic separation between transactional and marketing email.
Shared vs Dedicated IPs
When you send email through an Email Service Provider (ESP), your messages leave from either shared or dedicated IP addresses:
| Feature | Shared IP Pool | Dedicated IP |
|---|---|---|
| Reputation | Shared with other senders | Entirely yours |
| Volume requirement | Any volume | 50K+ emails/month |
| Warm-up needed | No (already warmed) | Yes (critical) |
| Cost | Included in ESP plan | Additional $20-50/month per IP |
| Control | Limited | Full |
If you send fewer than 50,000 emails per month, shared IPs from a reputable ESP are usually fine. Above that volume, dedicated IPs give you full control over your sending reputation.
IP Warm-Up Schedule
A new dedicated IP has no sending history. ISPs treat unknown IPs with suspicion. You must gradually build reputation by increasing volume over 2-4 weeks:
Week 1:
Day 1: 50 emails
Day 2: 100 emails
Day 3: 200 emails
Day 4: 400 emails
Day 5: 800 emails
Day 6: 1,500 emails
Day 7: 3,000 emails
Week 2:
Day 8: 5,000 emails
Day 9: 8,000 emails
Day 10: 12,000 emails
Day 11: 18,000 emails
Day 12: 25,000 emails
Day 13: 35,000 emails
Day 14: 50,000 emails
Weeks 3-4: Continue increasing 20-30% daily
until reaching target volume
During warm-up, send only to your most engaged subscribers first. High open rates signal to ISPs that your email is wanted.
IP Pools
Large senders use multiple IPs organized into pools for different email types:
Pool: Transactional (2 IPs)
├── 10.0.0.1 — Password resets, order confirmations, receipts
└── 10.0.0.2 — Account notifications, security alerts
Pool: Marketing (3 IPs)
├── 10.0.0.3 — Newsletter
├── 10.0.0.4 — Promotions
└── 10.0.0.5 — Re-engagement campaigns
Pool: Automated (1 IP)
└── 10.0.0.6 — Drip sequences, onboarding
Why Separate Pools
Transactional email (password resets, order confirmations) has near-100% engagement. Marketing email has 15-30% open rates and higher complaint rates. If both share the same IP, poor marketing engagement drags down the reputation for transactional delivery.
Separating pools ensures that a spike in marketing complaints does not cause password reset emails to go to spam.
Subdomain Strategy
Match your sending subdomains to your IP pools:
[email protected] → Transactional IP pool
[email protected] → Marketing IP pool
[email protected] → Automated IP pool
Each subdomain has its own SPF, DKIM, and DMARC records. This keeps reputation isolated at the DNS level as well.
Throughput and Rate Limiting
ISPs impose receiving rate limits — the number of messages they accept per hour from a single IP:
| ISP | Typical Limit (new IP) | Established IP |
|---|---|---|
| Gmail | ~500/hour | 10,000+/hour |
| Microsoft | ~1,000/hour | 10,000+/hour |
| Yahoo | ~1,000/hour | 5,000+/hour |
Your sending infrastructure must respect these limits:
# Postfix rate limiting example
# /etc/postfix/main.cf
smtp_destination_rate_delay = 2s
smtp_destination_concurrency_limit = 5
default_destination_rate_delay = 1s
Monitoring Infrastructure Health
Track these metrics for each IP:
- Delivery rate — Percentage of emails accepted (not bounced). Target: >98%.
- Inbox placement rate — Percentage that land in inbox vs spam. Use seed testing tools.
- Bounce rate — Hard bounces above 2% indicate list quality issues.
- Complaint rate — FBL complaints above 0.1% trigger ISP throttling.
- Blacklist status — Check daily via MXToolbox or similar monitoring.
Google Postmaster Tools and Microsoft SNDS provide free insight into how Gmail and Outlook view your sending reputation.