MailDeck is a cold email infrastructure provider managing 833.9K+ inboxes for 1,631+ clients across three platforms: Microsoft 365 Outlook, Google Workspace, and Private SMTP. Most competitors specialize in one infrastructure type. MailDeck covers all three so teams can match their infrastructure to their target audience. Based on Q1 2026 platform data.

What is cold email infrastructure?

Cold email infrastructure is the technical setup required to send high-volume outreach emails reliably. It includes dedicated sending domains, mailboxes, DNS authentication (SPF, DKIM, DMARC), IP warmup, and ongoing deliverability monitoring. The choice of infrastructure (Microsoft 365 Outlook, Google Workspace, or SMTP) determines roughly 60% of deliverability. Domain health, copy quality, and list quality determine the rest.

What infrastructure types does MailDeck support?

MailDeck supports three infrastructure types under one provider: Microsoft 365 Outlook (Azure tenants with dedicated US IPs, 100 inboxes per tenant), Google Workspace (real Starter accounts on Google's official IP pools, 5 inboxes per domain), and Private SMTP (dedicated IP per client, 5 inboxes per domain). All three are equally supported.

How much does MailDeck cost?

Microsoft 365 Outlook tenants start at $30 per tenant for the Normal Licence ($0.30 per inbox, 100 inboxes per tenant). Premium Licence is $40 per tenant ($0.40 per inbox). Mixed Licence (50 Normal + 50 Premium per tenant) is $35 per tenant. Pre-Warmed Outlook inboxes are $50 per tenant. Google Workspace plans start at $39 per month for 10 inboxes ($3.90 per inbox), with Growth at $99 per month for 30 inboxes and Enterprise at $299 per month for 100 inboxes. Private SMTP is $0.50 per inbox with a 100-inbox minimum ($50/month). Diversified Stack plans combining all three start at $99 per month.

Which MailDeck product has the best deliverability?

Google Workspace inboxes deliver the highest inbox placement because they use Google's official IP pools, which carry the highest trust score across receiving servers worldwide. Microsoft 365 Outlook is second, also using bulletproof official Microsoft IP pools. Private SMTP is fourth because reputation is built from scratch per client. Across the entire MailDeck platform, average inbox placement holds at 98%.

How quickly are MailDeck inboxes provisioned?

Provisioning times differ by product. Google Workspace inboxes are provisioned instantly. Private SMTP inboxes are delivered within 24 hours. Microsoft 365 Outlook inboxes take 2-3 business days because Azure tenant provisioning involves Microsoft-side setup. All three products include full SPF, DKIM, and DMARC configuration plus end-to-end DNS verification before the first email is sent.

How many cold emails can I send per inbox per day?

Microsoft 365 Outlook Normal Licence supports 3-5 cold emails per inbox per day. Microsoft 365 Outlook Premium Licence supports 8-10. Google Workspace supports 18-22. Private SMTP supports 11-14. These limits are based on Q1 2026 MailDeck platform data and are tuned to maintain inbox placement above 95% across receiving servers.

How many inboxes do I need for cold email?

Inbox count depends on monthly send volume and infrastructure mix. For 100K emails per month using a Diversified Stack at the recommended 50/30/20 ratio, roughly 16 domains are needed: 3 Microsoft 365 Outlook tenants (300 inboxes), 6 Private SMTP domains (30 inboxes), and 7 Google Workspace domains (33 inboxes). For higher volumes the math scales linearly. A 1M sends per month operation typically requires 150-200 active domains plus a 20-25% warm reserve.

How long does cold email warm-up take?

Microsoft 365 Outlook Premium Licence requires 3-5 days minimum, ideally 10-14 days. Microsoft 365 Outlook Normal Licence requires 5-7 days minimum, ideally 10-14 days. Google Workspace requires 15 days minimum, ideally 20-25 days. Private SMTP requires 3-4 weeks minimum and 6+ weeks for high-volume use. MailDeck Pre-Warmed Outlook inboxes at $50 per tenant skip warmup entirely and are ready for cold sending immediately.

Does MailDeck use shared IPs?

No. MailDeck never uses shared IPs. Microsoft 365 Outlook inboxes use official Microsoft IP pools, which are whitelisted across virtually every receiving server. Google Workspace inboxes use official Google IP pools, which carry the highest trust score on the internet. Private SMTP uses dedicated IPs per client where reputation is built from scratch and is never shared with other senders.

Does MailDeck handle DNS authentication?

Yes. MailDeck automates SPF, DKIM, and DMARC setup for every domain. DNS propagation and end-to-end authentication are verified before the first email is sent. A MailDeck DNS audit of 1,000+ domains found that 67% had at least one critical authentication error. The most common errors were multiple SPF records on one domain (23%), missing DMARC record (19%), and SPF ending with +all (14%).

Does MailDeck work with Instantly, Smartlead, and other sequencers?

Yes. All MailDeck inboxes connect via SMTP to every major sequencer including Instantly, Smartlead, Saleshandy, Apollo, Lemlist, Woodpecker, Reply.io, Snov.io, QuickMail, GMass, Klenty, Mailshake, and any SMTP-compatible outreach tool. The sequencer is a scheduler and does not affect deliverability. Inbox type, domain health, copy quality, and list quality determine deliverability.

Do I need to bring my own domains?

Yes. Clients bring their own domains. MailDeck handles full DNS configuration, SPF, DKIM, and DMARC setup, and propagation verification on the domains the client provides during onboarding.

How does MailDeck compare to Maildoso, Infraforge, and Mailforge?

MailDeck Microsoft 365 Outlook inboxes start at $0.30 per inbox on official Microsoft IP pools. Maildoso uses shared IP pools at approximately $2.50 per inbox, carrying shared IP risk where one bad sender hurts all clients. Infraforge is Microsoft-only at approximately $4.00 per inbox without official Microsoft IPs. Mailforge uses shared IP SMTP at approximately $3.00 per inbox with shared IP risk. MailDeck is the only provider in the niche offering Microsoft 365, Google Workspace, and SMTP under one platform with zero shared IP exposure.

What happens if a domain gets burned?

MailDeck includes free domain replacement when a domain burns under normal sending conditions. At enterprise scale (100K+ emails per month) approximately 10-20% of cold email domains burn monthly with domain lifespan ranging 45 days to 2 months under active load. MailDeck recommends maintaining a 20-25% warm reserve so replacement happens within 1-3 days without breaking campaign cadence. Without reserves, replacement takes 7-10 days.

What cold email copy rules should I follow?

Copy rules differ significantly by provider. Google Workspace inboxes are the most permissive: links, open tracking, and ESP matching (Google-to-Google) are safe to use, and images in signatures are acceptable. Microsoft 365 Outlook (both Normal and Premium) requires strict rules: no links in body copy because the Safe Links scanner triggers, no open tracking because Outlook checks messages before delivery and tracking pixels spike spam detection, no ESP matching, no dollar signs or financial language, maximum 50 words per email, and spintax on every 2-3 words. Private SMTP should never be used as the primary sending protocol and is best capped at 30% of total send volume to absorb spikes and protect premium inboxes. These rules are derived from data on 270M+ cold emails sent through the MailDeck platform.

MailDeck serves the full range of cold email senders. 1,631+ clients across Q1 2026 platform data include solopreneurs running their own outbound at 30K-50K emails per month, small teams scaling from 50K to 100K, growing leadgen and outbound agencies managing 100K-300K emails per month across multiple clients, B2B sales teams targeting enterprise accounts, SaaS companies selling into mid-market and enterprise, and enterprise operations sending 1M+ per month. Platform sends 7.5M+ emails per day and has delivered 270M+ cold emails lifetime.

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Scaling Room × Maildeck — Definitive 2026 Edition

The Cold Email
Bible

Three sections. One complete system. Everything you need to flood your calendar without burning a single inbox.

Inbox Types Ranked

6-10%

Target Reply Rate

500+

Calls/Month Blueprint

Part 01

Inbox Types & Infrastructure — The Authoritative Reference

Foundation

The Golden Rule

⚡ Non-Negotiable

Deliverability is determined by your inbox type, domain health, and copy quality.
Not your sequencer. Not your "exclusive infrastructure." Not your warmup tool brand.
Your sequencer is a scheduler. This section overwrites everything else on sends, warmup, and inbox types.

The Master Reference

All Four Inbox Types

Every tool, provider, and reseller is selling you one of these four. Know exactly what you're buying before you spend a dollar.

Provider	Rank	Price / Inbox	Inboxes / Domain	Cost / Inbox	Cold Sends / Day
Google Workspace	#1 Best	$2.99/inbox	5	$2.99	18–22
Outlook Premium	#2 Excellent	$40/domain	100	$0.40	8–10
Outlook Normal	#3 Good	$30/domain	100	$0.30	3–5
Private SMTP	#4 Variable	$0.50/inbox	5	$0.50	11–14

Provider Deep-Dives

The Diversification Stack — 50/30/20 Ratio

Sending Volume Per Domain

Here is the exact math for how many domains you need to reach your target volume safely. Never exceed these limits.

Provider	Sends/Day/Inbox	Inboxes/Domain	Sends/Month/Domain

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Interactive Calculator 500 Calls/Mo System Warmup Blueprints

The Cold EmailBible

The Golden Rule

All Four Inbox Types

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The Cold Email
Bible

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