DNS
What is Mail Transfer Agent Strict Transport Security (MTA-STS)?
A policy that forces inbound mail to your domain to be delivered over validated, encrypted TLS.
MTA-STS lets a domain publish a policy, advertised through a DNS TXT record and served over HTTPS, that requires sending MTAs to use TLS with a valid certificate when delivering to it. It closes a gap in opportunistic SMTP TLS, where an attacker could strip encryption or force a downgrade or man-in-the-middle attack. It is typically paired with TLS-RPT, which reports back on TLS negotiation and delivery failures.
Why it matters for cold email
MTA-STS mainly protects mail coming into your domain, such as prospect replies, rather than your outbound sends, but configuring it correctly signals a professionally maintained domain, which contributes to overall trust and reputation.
Related terms
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