Cloud vs On-Premise Email Security: Who Reads the Message?
Cloud email security scans mail in a vendor network. On-premise gateways scan on yours. A decision page for Mimecast-style MX versus Hexamail Guard.
The real difference is custody of the body
Cloud email security (Mimecast, Proofpoint, Barracuda Cloud, Microsoft Defender) receives the message, inspects it, then forwards. You buy expertise, continuity, and URL rewriting. You accept a processor.
On-premise (Hexamail Guard, SpamAssassin, appliance filters) inspects on your LAN. DNSBLs still phone home with hashes/IPs; the body stays. That is the on-premise spam filter cluster’s reason to exist.
Choose cloud when
Mail is already in Microsoft 365; you want vendor MX failover; nobody will patch a gateway; phishing training + API pull from M365 is the program.
Choose on-prem when
Policy forbids third-party body scan; Exchange/Hexamail/MDaemon is on-site; latency or sovereignty; you already operate Windows/Linux servers. Then Guard is the commercial SMTP gateway, Rspamd the DIY one.
app cta