Mimecast vs Microsoft 365 and Sophos for SMEs

For most Australian SMEs the honest answer to "Mimecast vs Microsoft 365" is that a properly configured Microsoft 365 setup, with Sophos added where it earns its place, covers email security without a separate gateway. Mimecast and Proofpoint are capable products, but they were built for a scale and a set of problems that many small businesses do not have. The right choice depends on what you already pay for, how complex your mail is, and your compliance obligations, not on which brand is best known.

Key facts

• Every Microsoft 365 mailbox includes Exchange Online Protection, and Business Premium adds Microsoft Defender for Office 365 Plan 1 (Safe Links, Safe Attachments, impersonation protection).
• Defender for Office 365 Plan 2, in the enterprise plans, adds phishing simulation, automated investigation, and threat hunting.
• Mimecast and Proofpoint are independent email security platforms with strong heritage in archiving, continuity, and large-scale filtering.
• A third-party gateway sits in front of or alongside Microsoft and adds an independent layer, which matters most at larger scale or under heavy compliance.
• 4iT uses Sophos for email and endpoint security and configures Microsoft's own tooling, choosing per client rather than defaulting to one product.
• For many SMEs the biggest gain is configuring the protection they already own, not buying another layer on top of a misconfigured one.

What you already get with Microsoft 365

Microsoft 365 includes more email security than most businesses realise, which changes the comparison before it starts. Every mailbox comes with Exchange Online Protection, which handles spam, bulk mail, and known malware. Microsoft 365 Business Premium adds Microsoft Defender for Office 365 Plan 1, which brings Safe Links, Safe Attachments, and impersonation protection, the controls that matter most against phishing and business email compromise. The enterprise plans, and the optional Defender add-on for Business Premium, include Plan 2, which adds phishing simulation, automated investigation and response, and threat hunting. The catch is that these are often left on defaults. Turned on and tuned with Microsoft's recommended security policies, the native stack is genuinely strong for an SME.

What do Mimecast and Proofpoint add?

Third-party gateways like Mimecast and Proofpoint add an independent security layer that does not depend on Microsoft, plus mature archiving and continuity features. They are cloud platforms that filter mail before or alongside Microsoft, and their heritage is in large-scale filtering, email archiving, and keeping mail flowing during an outage. That independence is the real argument for them: if you want email security that is not part of the same platform as your mailbox, a separate vendor gives you that separation. They also tend to have deep, granular controls that large or heavily regulated organisations value. The trade-off is cost and complexity. For a 15-person business, that depth is mostly capability you will never configure, on top of a Microsoft licence that already includes solid protection.

Mimecast vs Microsoft 365: which suits an Australian SME?

For the typical Sydney SME on Business Premium, the better first move is to configure Microsoft properly, not to add a gateway. We see businesses paying for a third-party filter while their Defender for Office 365 policies sit on defaults, which is the worst of both worlds: extra spend and weak configuration. A third-party gateway earns its place in specific cases: when you are large enough that the granular control and independent layer genuinely matter, when you have heavy archiving or compliance obligations that a dedicated platform handles better, when you run a mix of mail platforms rather than pure Microsoft 365, or when an insurer or contract requires a separate layer. Outside those cases, the money is usually better spent on configuration, multi-factor authentication, email authentication, and staff awareness.

Where Sophos fits, and how 4iT decides

We use Sophos for email and endpoint security because it gives SMEs strong protection that is managed from one place alongside their other cyber security, without enterprise pricing. But we do not lead with a product. The approach we take with every client is the same: get the Microsoft 365 protection you already pay for configured correctly first, add Sophos where an independent or unified layer adds real value, and only consider a heavyweight gateway like Mimecast or Proofpoint when the scale, compliance, or platform mix genuinely calls for it. That is the opposite of brand loyalty. The best email security is the one that fits your size and risk, configured properly, not the one with the biggest name. If I am being honest, most SME email incidents we see come down to missing MFA or a misconfigured tenant, not the absence of a premium filter.

Frequently asked questions

Is Microsoft 365 email security good enough without Mimecast?

For most SMEs, yes, once it is configured properly. Business Premium includes Defender for Office 365 Plan 1, which covers phishing, impersonation, and malicious links and attachments. The common failure is leaving it on defaults rather than applying the recommended security policies. A gateway adds value mainly at larger scale or under heavy compliance.

What does Mimecast do that Microsoft 365 does not?

Its main advantages are an independent security layer separate from Microsoft, mature email archiving and continuity, and very granular controls. Those matter most to larger or heavily regulated organisations. For a small business already on Business Premium, much of that is capability you will not use, on top of protection you already have.

Should we run both Microsoft Defender and a third-party gateway?

Some organisations do, for defence in depth or independence. For most SMEs it is overkill and adds cost and complexity. We would rather see Business Premium configured correctly with MFA and email authentication in place than a second product bolted onto a weak baseline.

What does 4iT recommend for SME email security?

Configure the Microsoft 365 protection you already pay for, enable MFA and impersonation protection, set up SPF, DKIM, and DMARC, and add Sophos where a unified or independent layer helps. We only recommend a heavyweight gateway when scale, compliance, or a mixed mail platform genuinely justifies it.

If you are weighing up a third-party email filter against what you already have in Microsoft 365, we can review your current setup and tell you honestly whether you need it. More often than not the better value is fixing the email and spam protection configuration you are already paying for, and that is a conversation we are happy to have.