What are email security gateways?
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Your company already has some email filtering built in. Google Workspace and Microsoft 365 both scan incoming mail for spam and known malware. So what does an email security gateway actually add on top of that?
An email security gateway is a dedicated filtering layer that sits between the internet and your mail server. Every message passes through it before it ever reaches a user's inbox. Think of it as a customs checkpoint that inspects everything coming in (and sometimes going out) before it's allowed through.
Where native filtering catches obvious spam and known threats, a gateway goes further. It scans attachments for malicious payloads, rewrites links so they can be checked at click time, enforces encryption policies, and flags phishing attempts that look legitimate on the surface. Enterprise-grade gateways also add sandboxing (opening suspicious files in an isolated environment to watch what they do) and data loss prevention (blocking employees from accidentally sending sensitive data out).
The big names you'll run into are Barracuda, Mimecast, Proofpoint, and Microsoft Defender for Office 365. Some run as cloud services. Others are physical appliances you install on your network. Microsoft Defender sits inside the Microsoft 365 ecosystem itself.
So do you actually need one? It depends. A 10-person startup using Google Workspace probably doesn't. A 500-person company in finance, healthcare, or legal almost certainly does, because the threat surface is larger and the compliance requirements are stricter. The honest answer is that gateways add real protection but also add complexity. Overly aggressive filtering can rewrite legitimate links in ways that break click tracking and confuse your deliverability data. That's worth knowing before you buy.
If you're trying to figure out whether your current setup has gaps, our free email header analyzer can show you what authentication checks are already happening on your inbound mail. Or if you'd rather just talk it through, the SOS hotline is free.
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