Secure Email Gateways act as intermediaries between the internet and an organization's email infrastructure, scanning all email traffic before delivery.
How SEGs work
- MX records redirect email to the gateway before reaching the mail server.
- Messages are scanned for threats, spam, and policy violations.
- Clean emails are forwarded to the destination; threats are quarantined or rejected.
- Outbound emails are checked for sensitive data and policy compliance.
Core capabilities
- Anti-spam: Filters bulk mail and unsolicited messages.
- Anti-phishing: Detects impersonation and credential theft attempts.
- Anti-malware: Scans attachments and blocks malicious files.
- URL rewriting: Rewrites links for time-of-click scanning.
- DLP: Prevents sensitive data from leaving via email.
- Encryption: Policy-based email encryption for compliance.
SEG vs API-based security
- SEG (MX-based): Sits in front of email infrastructure, requires DNS changes.
- API-based (ICES): Integrates directly with cloud email via APIs, no MX changes needed.
- SEGs work well for on-premises Exchange; API solutions better suit cloud-native platforms like Google Workspace and Microsoft 365.
Deployment considerations
- MX record changes require careful planning for TTL propagation.
- Gateway IP whitelisting needed in cloud email platforms.
- May conflict with native security features in cloud email.
- Internal email visibility requires additional configuration (hair-pinning).
Leading vendors
- Proofpoint, Mimecast, Barracuda, Cisco ESA for traditional SEGs.
- Check Point Harmony, Abnormal Security for API-based approaches.
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Email authentication method that uses cryptographic signatures to verify that email content has not been tampered with in transit.
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Email validation system that builds on SPF and DKIM to prevent email spoofing and provide reporting on email authentication failures.
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A set of protocols (SPF, DKIM, DMARC) that verify the sender of an email is who they claim to be, preventing spoofing and phishing.
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Metadata attached to emails that shows routing information, authentication results, and delivery path.
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API-based email security solutions that integrate directly with cloud email platforms like Google Workspace and Microsoft 365, rather than routing mail through an external gateway.
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Email authentication method that specifies which mail servers are authorized to send email on behalf of your domain.
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