Microsoft Deliverability 101

Heyo 👋 

Let’s talk about the #1 Outbound killer - Microsoft Deliverability.

You always have at least 30-35% of recipients who use Microsoft, and they barely see your cold emails.

(If you’re targeting bigger companies, this % is even higher 😟)

Why?

Microsoft filters are stricter, their scoring is harsher, and most teams still optimize only for Gmail.

After managing 15,000+ mailboxes across Growth.band campaigns, here’s the hard truth:

Outlook is where most cold email strategies die 😵 

The Microsoft Problem

Most “deliverability guides” focus entirely on Gmail.

But Outlook and Exchange operate with an entirely different rulebook:

• Zero tolerance policy: Google gives warnings. Microsoft skips straight to spam.

• New domain penalty: Fresh domains without perfect setup are flagged instantly.

• Internal spam score: A private 0–10 score that’s far stricter than Google’s.

• Warm-up blindspot: Most tools only warm up Gmail, leaving Outlook cold.

And if you think “hey Ilya, I’ll just set up Microsoft mailboxes instead of Google - and it should be fine” - no.

Currently, there is no significant difference in deliverability between Google and Microsoft, or between Microsoft and Google.

What Kills Microsoft Deliverability

• Template-based copy detected by AI filters.

• Basic spintax that isn’t truly randomized.

• Consumer-grade SMTP setups.

• Missing or broken SPF/DKIM/DMARC records.

The result?

Burned domains. Dead campaigns. “Cold email is dead” posts on LinkedIn 😄 

✅ But here is the thing - we manage 15k+ mailboxes for our clients (if you need help with deliverability, reach out) - and we cracked MS filters - with a unique approach.

🔥 Our clients usually get 3.5x better reply rate from MS recipients using this set-up.

The Setup That Actually Works

After testing thousands of inboxes, this is the only reliable infrastructure for Microsoft deliverability:

🧰 Infrastructure:

→ Azure SMTP with enterprise IP reputation

→ 1 domain = 10 mailboxes = 50 cold emails/day max

→ 20% of the infra is dedicated for the rotation

☕️ Warm-up:

→ Separate pools for Gmail vs Microsoft

→ Use premium warm-up tools built for Outlook

🖥️ Technical:

→ Perfect DNS authentication

→ Microsoft-specific inbox placement testing

→ ESP matching (send Azure SMTP → Microsoft)

🧪 Testing Protocol

Run deliverability tests bi-weekly, not “never”.

→ Include Outlook in every inbox placement test

→ Monitor each ESP separately

→ Rotate domains proactively when issues appear

The goal: stay ahead of Microsoft’s hidden spam score before it tanks your domain.

💰 The Hard Truth

This setup costs 2–3x more than your average cold email system.

But burning through domains and destroying your sender reputation?

That costs way more.

🚩 Common Mistakes to Avoid

• Using shared SMTP servers

• Using Google mailboxes to reach out to MS

• Only testing on Gmail

• Sending identical content across domains

• Ignoring Microsoft-specific warm-ups

Avoid these, and your deliverability rate instantly jumps.

📊 Metrics That Actually Matter

→ Inbox rate for Outlook/Exchange users

→ Microsoft spam score trend

→ Domain reputation across both ESPs

If you’re serious about cold email in 2025, these are the KPIs that matter - not just “reply rates.”

🔐 Bonus: Enterprise SPAM Shields

If your recipients use Mimecast or Proofpoint, you need Azure SMTP with enterprise IPs.

At least with the proper infra, you get some chances; otherwise, even your best-crafted emails never make it out of the sandbox.

🎓 Want to Go Deeper?

I’m hosting a free live session on:

The Cold Email Infrastructure System Behind 15,000+ Mailboxes [99%+ Inbox Rate]

We’ll cover:

• ✅ Step-by-step technical setup

• ✅ Warm-up strategy for Microsoft

• ✅ Real inbox placement examples

• ✅ Scalable systems for agencies & founders

👉 Register for the webinar here.

If you send cold emails - this session will save your campaigns in 2025.

—

With 🫰to your Growth,

Ilya (let’s connect on LinkedIn)