If you want to send 1 million cold emails a month, here's what you need.
Quick Maths
Azure Communication Services (ACS) capacity per slot:
- ~100,000 emails per month
- 4 domains per slot
- 100 inboxes per domain (400 total)
- Pre-warmed IPs (no IP warmup needed)
To hit 1 million emails:
- 1,000,000 ÷ 100,000 = 10 slots
- Agency plan includes 2 base slots
- 8 add-on slots needed at $49/mo each (BYOA)
Option 1: All ACS Pre-Warmed IP Track
What you need:
- 10 Infra Bundle slots (~$2/month to Azure with BYOA)
- ColdSend Agency plan + 8 add-on slots
How it works:
- Every domain stays on ACS permanently
- All inboxes use pre-warmed Azure IPs
- No external inboxes needed
The catch: Managing 10+ slots across Azure accounts is annoying, assuming you can somehow make them. But if you can, then all you need to watch out for is not getting caught by Azure ... we recommend using different billing details just to be safe.
Best for: Short-term blasts, proof of concept, or if you want all your volume on pre-warmed IPs.
Option 2: The Rotation Strategy (Recommended)
What you need:
- 4 domains on ACS at any given time (1 slot)
- External inboxes (Google Workspace, Outlook, SMTP) for the rest
- ColdSend Growth or Scale plan (1 slot, 100K sends)
How it works:
- Month 1-2: Run campaigns on ACS domains (5–30 emails/day per inbox, building reputation)
- Month 2-3: Domains reach "Medium" or "High" reputation in Google Postmaster
- Month 3: Move those warmed domains to Google Workspace/Outlook
- Put fresh domains on ACS, repeat cycle
Why this works:
- ACS becomes your reputation accelerator, not your permanent infrastructure
- Once domains have reputation, they perform fine on standard infrastructure
- You scale indefinitely without adding more Azure accounts
Best for: Agencies, ongoing high-volume operations, sanity.
Read the full rotation playbook: Cold Email Without Warmup: The Complete 2026 Strategy
How We Differ from Instantly, Smartlead, etc.
Infrastructure, not features.
ColdSend is built on Azure Communication Services (ACS). ACS is a transactional email API—same infrastructure that sends your password resets and shipping notifications. These are pre-warmed, enterprise-grade IP pools reserved for critical mail.
The difference:
- ACS is one-way by design (send-only, no replies)
- We made it two-way by building a reply handling infrastructure on top
- We added guardrails (campaign auto-pauses at 4% bounce rate) so you don't violate ACS terms and get restricted
Most sequencers just connect to Gmail/Outlook APIs and hope your warmup works. We started with enterprise infrastructure and built sequencing on top.
What You'll Actually Pay
Complete No-Warmup Track:
Rotation Strategy:
For rotation, external inboxes vary by provider. Google Workspace is ~$6-12/user depending on your plan. If you're rotating 40+ domains through a cycle, you'll need to factor inbox costs during the migration phases. Also, given the limits on Google/Outlook inboxes, you'll need a lot more domains here. Assuming 25 inboxes per domain with 25 emails sent per day per inbox, you'll need approximately 54 domains to hit the same volume. And these are generous figures. We recommend at least 100 domains and lower sending volume. Mix and match as per comfort level, we don't have concrete numbers here. You can also just buy more add-on slots to offload some of the sending volume to that. Book a call with us if you wanna do a deep-dive.
The Reality Check
No one has sent 1 million emails through our ACS infrastructure yet. Individually, that is. Collectively, we have.
We'll be honest: at this volume, we need to work closely with you. The guardrails exist, but 1M emails/month puts you in territory where:
- List quality matters more than infrastructure
- Small bounce rate changes have big impacts
- Provider relationships matter
If you're serious about this volume, join our Discord first. We'll review your use case, your list sources, and your campaign approach before you commit.
What we don't have yet:
- CRM integrations (on roadmap; we can build one with you after reviewing your case)
- Done-for-you copywriting (but we can refer you to vetted writers in our community; we have a lot of talent there)
Quick Summary
The rotation strategy is more work upfront but significantly more sustainable. The all-ACS track works if you need pre-warmed IPs across all volume and don't mind managing multiple Azure accounts.
Try the buying guide → | Join Discord to discuss high-volume setup →
