https://www.proofpoint.com/us/products/email-security-and-protection/secure-email-relay
Secure Email Relay Service: SMTP Relay | Proofpoint US
May 13, 2026 - Secure transactional email with Proofpoint Secure Email Relay service. Migrate on-prem to cloud, centralize SMTP control, protect domains, and accelerate DMARC...
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https://www.authsmtp.com/
Outgoing authenticated SMTP server and email relay service (solves most SMTP and email relay...
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