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Microsoft 365 Guide

Microsoft 365 Mailbox Types Explained

A complete guide to choosing the right mailbox for your business. Stop overpaying for licenses and close security gaps with proper mailbox design.

⚠️ Why This Matters

  • Security gaps from wrong mailbox choices
  • Compliance failures in regulated industries
  • Higher licensing costs than necessary
  • Poor customer experience from email mismanagement

💡 Mailbox design is a business decision, not just an IT task.

📬 Understanding Each Mailbox Type

Microsoft 365 offers several mailbox types, each designed for specific purposes. Here’s what each one does and when to use it.

👤

User Mailbox

✓ External emails ✓ Internal emails ✓ Individual ownership
Best For
  • Employees
  • Leadership
  • Admin accounts
⚠️ Not for shared or team email needs
👥

Shared Mailbox

✓ External + internal ✓ Multiple users access ✓ No license needed (≤50GB)
Best For
  • Customer support
  • HR / Finance
  • IT Helpdesk
📧 Example: support@company.com
📢

Distribution List

✓ External + internal ✕ No mailbox storage ✕ No reply capability
Best For
  • Announcements
  • Broadcasts
  • One-way communication
📧 Example: all@company.com
🔗

Microsoft 365 Group

✓ Shared mailbox ✓ SharePoint files ✓ Teams integration
Best For
  • Project teams
  • Cross-functional work
  • External collaboration
💡 Email + Files + Chat in one place
🛡️

Mail-Enabled Security Group

⚡ External optional ✓ Internal emails ✓ Access control
Best For
  • Access control
  • Security alerts
  • Targeted notifications
🔐 Identity + access + communication combined
🏢

Room & Equipment Mailbox

✕ No external emails ✓ Internal booking ✓ Auto-scheduling
Best For
  • Meeting rooms
  • Projectors
  • Company vehicles
📅 Auto-booking through Outlook calendar
🌐

Mail Contact & Mail User (External/Hybrid)

✕ No external mail reception ✓ Internal visibility ✓ Appears in GAL
Best For
  • Vendors
  • Partners
  • Hybrid/on-prem users
  • External contacts in address book
📇 Shows external email addresses in your Global Address List

🧭 Quick Decision Framework

Match your need to the right mailbox type in seconds.

One Person
↓
User Mailbox
Team Inbox
↓
Shared Mailbox
Broadcast Only
↓
Distribution List
Collaboration
↓
M365 Group + Teams
Resources
↓
Room / Equipment

📋 Feature Comparison at a Glance

Not sure which mailbox fits your scenario? This comparison shows the key differences.

Mailbox Type External Email Internal Email Storage License Required
👤 User Mailbox ✓ ✓ 50-100GB Yes
👥 Shared Mailbox ✓ ✓ 50GB free No*
📢 Distribution List ✓ ✓ None No
🔗 M365 Group ✓ ✓ 50GB No
🛡️ Security Group Optional ✓ None No
🏢 Room/Equipment ✕ ✓ 50GB No
🌐 Mail Contact ✕ ✓ None No

*License required if storage exceeds 50GB or archive/legal hold features needed

💡 Key Insight

For organisations with 300+ users, mailbox architecture becomes critical. Poor planning leads to compliance issues, security vulnerabilities, and wasted license spend. A proper governance framework should be established before scaling.

Want to Learn More?

I regularly share insights on these Microsoft 365 topics:

📊Enterprise mailbox governance
🔒Security & DLP mapping
🎯M365 architecture best practices
🏗️Large tenant design (300+ users)

Need Help With Your M365 Mailbox Strategy?

At MStack360, we help businesses design mailbox architectures that reduce costs, improve security, and scale properly. Let’s discuss your setup.

📅 Book a Consultation
AM

Ahmed Masoud

Microsoft 365 Consultant | MStack360

Specialising in M365 migration, automation, and ongoing support. I help businesses escape IT provider headaches and build secure, scalable Microsoft 365 environments.

💼 LinkedIn ▶️ YouTube

 

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