Why the perimeter is no longer the control that matters most

Short answer (for a remote‑first SMB on Microsoft 365 Business Premium that’s configured well):
For most scenarios, you do not need an expensive, next‑gen/UTM hardware firewall at every site. A basic, reliable edge router/firewall for NAT, stateful filtering, and ISP failover is usually sufficient—provided you shift protection to identity, device and app layers using Business Premium’s built‑in controls (Intune, Microsoft Defender for Business, and Conditional Access) and keep Windows Defender Firewall always on and centrally managed. [1][2][3][4]

Why the perimeter is no longer the control that matters most

Remote work + SaaS have moved users and data outside the office network. Microsoft’s Zero Trust approach puts the control points at identity, device health, and applications, not at a single network chokepoint. Business Premium packages these controls for SMBs: Endpoint EDR/ASR and network/web protection on the device (Defender for Business), Conditional Access to gate app access, and Defender for Office 365 to neutralise email‑borne attacks. In other words: you inspect and block at the endpoint and the cloud, which significantly reduces the value of a costly on‑prem firewall for a typical remote workforce. [5][1][6]

Defender for Business (MDB) adds web protection, network protection, web content filtering, attack surface reduction (ASR), and EDR—controls that used to be sold as “firewall features” in branch appliances. These run on the endpoint and follow the user everywhere. [2][5]
Windows Defender Firewall should remain enabled and centrally configured via Intune security baselines—giving you host‑based segmentation and policy without paying for advanced edge appliances. [7][4]
Conditional Access (Entra ID P1) lets you require MFA and compliant devices for Exchange/SharePoint/Teams and other SaaS apps, blocking risky sign‑ins even if a user is “on the office network.” [8][9]
Defender for Office 365 (Plan 1) (Safe Links/Attachments, anti‑phishing) removes the single biggest ingress vector—malicious email—before it ever hits a device. [10]

So… is anything beyond a basic firewall required?

For a typical SMB with many remote workers and no critical on‑prem apps, the cost‑effective pattern is:

Keep a simple edge: ISP router/basic firewall with NAT, DHCP, basic filtering, and failover.
Do the heavy lifting in M365: Intune + Defender for Business + Conditional Access + Defender for Office 365.
Optionally add Microsoft’s cloud‑delivered network security (SSE) if you want SWG/Zero‑Trust Network Access without hardware (see below). [11]

This “thin‑edge, strong‑endpoint” model routinely outperforms legacy “big firewall, flat endpoints” setups in both risk reduction and TCO for remote‑first SMBs—because controls travel with the user and are enforced before data is accessed. [5][1]

When a high‑priced firewall might still be justified

Choose a premium firewall/UTM only if you truly need capabilities that are network‑only and site‑centric, for example:

High‑throughput site‑to‑site VPNs/SD‑WAN, or numerous branch tunnels to on‑prem resources you’ll keep long term.
Strict network segmentation/IPS for OT/IoT or lab environments that cannot run endpoint controls.
Regulatory demands for on‑prem IDS/IPS or mandated perimeter logging at a specific site.
Complex public services hosted in your office (reverse proxying/WAF for internet‑facing apps).

If none of these apply, put your budget into endpoint, identity, and app security rather than into an oversized edge box.

A practical blueprint: Configure Business Premium to replace “firewall features”

Below is a concrete, field‑tested setup that reduces or eliminates reliance on dedicated firewall appliances for most SMBs. I’ve mapped each step to the relevant Business Premium capability and included sources you already have.

1) Device hardening & local firewall (Intune + MDB)

Deploy Intune Security Baseline for Windows; enforce Windows Defender Firewall (all profiles), BitLocker, Windows Hello, credential guard, disable legacy protocols. [7]
In Defender for Business, enable:
- Network protection (block mode) to stop outbound calls to malicious domains from any app.
- Web content filtering to block risky categories (e.g., malware, proxies, adult, gambling) on the device.
- ASR rules (e.g., block Office from creating child processes; block credential theft).
- EDR with Automated Investigation & Remediation. [2][5]

These controls deliver the “URL filtering,” “DNS security,” and “IPS‑like prevention” marketing bullets you’d otherwise buy in a firewall—except they work everywhere the user goes. [6]

2) Identity gate (Entra ID Conditional Access)

Require MFA for all users (break‑glass excluded).
Require compliant device for Exchange, SharePoint, Teams; block legacy auth; add sign‑in risk and location conditions if needed.
Use App Protection Policies for BYOD to keep corporate data in protected app containers. [8][12]

3) Email & collaboration ingress (Defender for Office 365)

Turn on Safe Links and Safe Attachments with Dynamic Delivery; enable anti‑phishing and impersonation protection; route high confidence spam to quarantine. [10][13]

4) “Always‑on” local firewall

Ensure Windows Defender Firewall is on (even if another firewall exists). Manage via Intune; never disable it as a shortcut. [4]

5) Verification & posture

Track and remediate via Microsoft Secure Score and Defender for Business TVM dashboards; use the Business Premium setup checklists to close gaps. [3][14]

Want a cloud alternative to hardware perimeter security?

If you still want centralised egress policy and VPN‑less private app access—without buying boxes—Microsoft now offers Security Service Edge (SSE) under Global Secure Access:

Microsoft Entra Internet Access = identity‑aware Secure Web Gateway for internet/SaaS (generally available).
Microsoft Entra Private Access = Zero‑Trust Network Access that can replace traditional VPNs for private apps. [11][15][16][17]

These are add‑ons (not bundled with Business Premium), but they’re often cheaper and simpler than rolling out/maintaining premium branch firewalls, especially for multi‑site SMBs. [11]

Decision framework (quick)

Remote‑first, SaaS‑first, no critical on‑prem:
Go basic edge + Business Premium blueprint above. No high‑priced firewall required. [1][2]
Some on‑prem, but limited:
Consider basic edge + Entra Private Access for VPN‑less private access. Add Entra Internet Access if you need centralised web policy/logging across sites. [11][16]
Heavy on‑prem/OT, compliance‑driven, or high‑throughput site mesh:
A premium firewall/UTM may be justified—ideally fewer, centralised ones—combined with the Business Premium controls above.

Put it into action in 2–3 weeks (what I’d run for your clients)

Baseline: Deploy Intune security baseline and onboard all devices to Defender for Business; verify Network protection and Web filtering are in block mode. [7][2]
Conditional Access: Enforce MFA + compliant device for Exchange/SharePoint/Teams; block legacy auth. [8]
MDO: Switch to Strict presets for Safe Links/Attachments and anti‑phishing; set HC spam/quarantine. [10]
Windows Firewall: Confirm enabled across all profiles; centrally manage rules; audit for exceptions. [4]
Review: Raise Secure Score; close top recs; report back with MDB/MDO incident stats to demonstrate risk reduction. [14]

References you already have on hand

Microsoft Defender for Business A Comprehensive Guide to Endpoint Protection, Capabilities, and Comparison with Defender for Endpoint Plans — details Network protection, Web protection, Network firewall integration and ASR/EDR scope. [2]
Module 02 – Security and Microsoft-Defender-for-Business-Licensing-Basics-and-Comparison — summary of MDB capabilities mapped to NIST and Business Premium. [1][18]
Roadmap for Security in Microsoft 365 Business Premium and Microsoft 365 Business Premium Setup Checklist A Comprehensive Guide for IT Professionals — step‑by‑step configuration roadmap. [10][19]
Microsoft Learn: Secure managed devices with Business Premium, Keep Windows Defender Firewall on, and Global Secure Access (Entra Internet/Private Access).
Learn article [20] · Windows Defender Firewall guidance [4] · Global Secure Access overview [11] · Entra Internet Access GA announcement [15]

Bottom line

For most remote‑heavy SMBs standardising on Microsoft 365 Business Premium, spend on configuring Business Premium properly and keeping Windows Defender Firewall enforced, not on premium hardware firewalls. Use Global Secure Access if/when you need cloud‑delivered SWG/Zero‑Trust access. Keep hardware at the edge simple unless you have clear, site‑specific needs that only a high‑end firewall can meet. [1][2][11]

If you like, I can turn this into a client‑ready one‑pager with a policy checklist you can drop into proposals, plus an Intune/MDB baseline JSON to deploy across tenants. Want me to draft that?

References

[1] Module 02 – Security

[2] Microsoft Defender for Business A Comprehensive Guide to Endpoint Protection, Capabilities, and Comparison with Defender for Endpoint Plans

[3] Microsoft 365 Business Premium Setup Checklist A Comprehensive Guide for IT Professionals

[4] Protect unmanaged devices with Microsoft 365 Business Premium

[5] Renew-and-Upsell-SMB-Customers-with-Microsoft-365-Business-Premium-and-Microsoft-Defender-for-Business English Deck 1

[6] 17 – Threat Protection Engagement – Microsoft Defender for Endpoint and Microsoft Defender Vulnerability Management Overview

[7] Roadmap to Mastering Microsoft Intune & Device Management (M365 Business Premium)

[8] How Conditional Access Works in M365 Business Premium

[9] Roadmap to Mastering Microsoft Intune & Device Management (M365 Business Premium)

[10] Roadmap for Security in Microsoft 365 Business Premium

[11] What is Global Secure Access? – learn.microsoft.com