Microsoft 365 Business Premium vs E3: Which Plan Fits?

Microsoft 365 Business Premium is the better plan for almost any organization under 300 users, and the reason surprises people: on security it includes more than E3, not less. Business Premium bundles Defender for Business (endpoint detection and response) and Defender for Office 365 Plan 1 (link and attachment protection) along with Intune and Entra ID P1. Microsoft 365 E3 has no user cap and adds enterprise features such as Windows Enterprise, larger mailboxes and eDiscovery, but its endpoint protection is the lighter Defender for Endpoint Plan 1 and its email protection is the basic Exchange Online Protection. Move to E3 when you pass the cap or need those enterprise features; move to E5 when you need the full security suite. This article lays out the differences and the licensing paths between them.

What is the difference between Business Premium and E3?

Both plans give every user the Office apps, Exchange email, OneDrive and SharePoint, Intune for device management and Entra ID P1 for Conditional Access. The differences are in three places: who may buy the plan, what security is bundled, and which enterprise extras are included. Microsoft lists the Business plans on its business plan comparison page and the enterprise plans on its enterprise plans page; both change, so treat those pages as the authority and this article as the explanation.

If you are still deciding between Business Standard and Business Premium, that is a different question, and we answered it in Business Premium vs Standard. This article assumes you want the security Premium provides and are asking whether the enterprise plan is the next step.

Which plan has better security?

Business Premium, at this tier. It includes Defender for Business, which is endpoint detection and response with automated investigation, attack surface reduction rules and vulnerability management, designed by Microsoft for companies up to 300 employees. It also includes Defender for Office 365 Plan 1, which adds Safe Links and Safe Attachments scanning to email and Teams, and anti-phishing policies that catch impersonation of your executives and your domain.

Microsoft 365 E3 includes Defender for Endpoint Plan 1, which covers next-generation antivirus, attack surface reduction and device control but stops short of the detection and response and automated investigation that make EDR useful in an incident. Its email protection is Exchange Online Protection, the baseline filter every Exchange Online mailbox gets. To match what Premium includes on endpoints and email, an E3 customer adds Defender for Endpoint Plan 2 and Defender for Office 365, buys the E5 Security add-on, or moves to E5.

That is why we tell clients not to think of E3 as an upgrade in protection. It is an upgrade in scale and enterprise features. A 40-person accounting firm on E3 has weaker email and endpoint defenses than the same firm on Business Premium, unless it has bought add-ons. Our Microsoft 365 security checklist shows what to turn on in Premium, and most of it is included in the plan.

What does the 300-user cap really mean?

Each Business plan (Basic, Standard, Premium) allows up to 300 licensed users. A company with 250 people is fine. A company with 320 cannot license all of them on Premium. The cap counts licensed users, not employees or mailboxes, so shared mailboxes and resource accounts are not the issue; people who need a seat are. Microsoft permits mixing Business and Enterprise plans in one tenant, so the usual path for a company crossing the line is Business Premium for the first 300 users and E3 or E5 for the rest, or frontline F-series licenses for staff who need only email and Teams on a phone.

The cap also shapes planning. A company at 240 people that expects to hire 100 next year should decide now whether the whole organization moves to an enterprise plan at once or runs a mixed tenant, because policies, security baselines and Copilot decisions get harder to keep consistent when the plans differ. Neither choice is wrong. Mixed tenants are common and supported; the work is in documentation.

What does E3 offer that Business Premium does not?

Windows Enterprise is the headline. E3 licenses Windows Enterprise edition, which adds management and security features beyond Pro, including capabilities that larger organizations and some compliance frameworks expect. Business Premium provides upgrade rights to the Business editions of Windows, which are Pro-level.

E3 mailboxes are larger, which matters for firms that keep years of email in the primary mailbox rather than the archive. E3 includes eDiscovery (Standard) and broader Purview compliance tooling, which legal and financial firms use to respond to holds and requests. Some Purview features, along with audit log retention beyond the default, are enterprise-only or E5-only, so check the specific feature you need against the plan page rather than assuming. E3 is also the plan on which large-organization purchasing options such as Enterprise Agreements are available, while Business Premium is bought through a Cloud Solution Provider partner or directly from Microsoft.

Teams is now a line item on both. Since 2024 Microsoft has sold the enterprise suites to new customers without Teams, with Teams Enterprise licensed separately, and the Business plans are offered in versions with and without Teams. Existing subscribers have transition options that depend on when they bought, which is one more reason to review licensing with someone who does it every week. Our post on the 2026 Microsoft 365 price changes covers what moved and when.

What are the licensing paths when you outgrow Premium?

There are four sensible routes. First, mix: keep Business Premium for up to 300 users and add E3 for the overflow, keeping in mind that the E3 users have lighter security unless you add Defender for Endpoint Plan 2 and Defender for Office 365 for them. Second, move everyone to E3 and add the E5 Security add-on, which brings Defender for Endpoint Plan 2, Defender for Office 365 Plan 2, Defender for Identity, Defender for Cloud Apps and Entra ID P2 without the full E5 price. Third, move everyone to E5, which includes all of that plus Teams Phone capability, Power BI Pro and the premium Purview features; this is the right answer for regulated firms that will use them. Fourth, stay on Premium and use frontline licenses for staff who need only mail and Teams on a phone, which keeps many companies under the cap for years.

Whichever route, do the switch as a project: map every user to a plan, confirm which security policies depend on which license, and schedule the change so nobody loses a feature mid-week. Conditional Access policies, Intune enrollment and Defender onboarding all key off licenses, and a license swap done carelessly can silently drop a device out of protection. Our Conditional Access guide explains the dependencies.

Which plan fits your business?

Under 300 users with no specific enterprise requirement: Business Premium, fully configured. Under 300 users with a need for Windows Enterprise, large primary mailboxes or eDiscovery: E3 plus the security add-ons, or E5 if you will use the full suite. Over 300 users: E3 or E5 for everyone, or a mixed tenant with Premium for the first 300, chosen based on how much consistency you need across policies. If Copilot is on the roadmap, note that the Copilot license options differ between Business and Enterprise plans; our Business Copilot plans FAQ has the current shape.

Frequently asked questions

Is Microsoft 365 E3 better than Business Premium?

Not on security. Business Premium includes Defender for Business with endpoint detection and response and Defender for Office 365 Plan 1, while E3 includes the lighter Defender for Endpoint Plan 1 and basic Exchange Online Protection. E3 is better on scale and enterprise features: no user cap, Windows Enterprise, larger mailboxes and eDiscovery. Choose by what you need, and add security to E3 if you take that route.

Can we mix Business Premium and E3 in one tenant?

Yes. Microsoft allows Business and Enterprise plans to coexist in the same tenant, and mixing is the common path for companies crossing the 300-user line. The work is in keeping security consistent, because the two plans include different Defender products, and in documenting which users hold which license so Conditional Access, Intune and Copilot decisions stay predictable.

Does E3 include Defender for Business?

No. Defender for Business is bundled with Business Premium and sold standalone for other plans. Microsoft 365 E3 includes Defender for Endpoint Plan 1, which lacks the detection and response features. E3 customers who want EDR typically add Defender for Endpoint Plan 2, buy the E5 Security add-on, or move to E5, each of which provides the enterprise version of the same protection.

When should a business move from Business Premium to E5?

When it passes 300 users and wants the full security suite, or when it needs features only E5 includes, such as Defender for Identity, Defender for Cloud Apps, Entra ID P2 for privileged identity management, premium Purview compliance or Teams Phone capability. Regulated firms in finance and healthcare often justify E5 on those features alone; a general office rarely does.

Licensing is the part of Microsoft 365 that most often goes wrong quietly, with security features paid for and never turned on, or users on the wrong plan for years. Our Microsoft 365 management service reviews every license against what each user needs, configures the security the plan already includes, and manages the tenant month to month, with Microsoft 365 security hardening as part of the same agreement. Send us your current license list and we will tell you what fits, and what you are paying for without using.