Probing TLS endpoints...

SMTP TLS Posture Check for mailgun.net — Relaymetry

STARTTLS extends SMTP with opportunistic encryption. A mail server advertises STARTTLS during the EHLO handshake, and sending systems can negotiate TLS for the message body. Modern operators expect TLS 1.2 minimum; TLS 1.0 / 1.1 are deprecated.

SMTP TLS Posture Check for mailgun.net

TLS configured with non-fatal issues.

Outbound submission TLS posture

TLS configuration looks healthy.

via heuristic `smtp.mailgun.net`

Submission (port 587 / STARTTLS)

TLS configuration looks healthy.

TLS version: TLSv1.3
Cipher: TLS_AES_128_GCM_SHA256The cipher suite is the algorithm pair used for key exchange and data encryption in a TLS session. Learn more →

Certificate

Subject: CN=*.mailgun.org,O=MAILGUN TECHNOLOGIES, INC,L=San Antonio,ST=Texas,C=US
SAN: *.mailgun.org, mailgun.org
Issuer: CN=DigiCert Global G2 TLS RSA SHA256 2020 CA1,O=DigiCert Inc,C=US
Valid from: 2026-03-18T00:00:00.000Z
Valid to: 2026-10-02T23:59:59.000Z
Expires in: 46 days
Fingerprint: 71:57:9D:50:7D:39:8F:CC…

SAN does not include MX host

SMTPS (port 465 / Implicit TLS)

TLS configuration looks healthy.

TLS version: TLSv1.2
Cipher: ECDHE-RSA-AES128-GCM-SHA256The cipher suite is the algorithm pair used for key exchange and data encryption in a TLS session. Learn more →

Certificate

Subject: CN=*.mailgun.org,O=MAILGUN TECHNOLOGIES, INC,L=San Antonio,ST=Texas,C=US
SAN: *.mailgun.org, mailgun.org
Issuer: CN=DigiCert Global G2 TLS RSA SHA256 2020 CA1,O=DigiCert Inc,C=US
Valid from: 2026-03-18T00:00:00.000Z
Valid to: 2026-10-02T23:59:59.000Z
Expires in: 46 days
Fingerprint: 71:57:9D:50:7D:39:8F:CC…

SAN does not include MX host

Inbound MX TLS posture (announced)

TLS configured with non-fatal issues.

MTA-STS policy

MTA-STS not published

TLS-RPT (reporting)

TLS-RPT not published

The result above probes the domains primary MX hosts on ports 25 + 587 (or whichever the domain uses) and reports the TLS version negotiated, certificate validity, SAN match status, and whether MTA-STS / TLS-RPT policies are published.

Configure TLS 1.2 minimum; aim for TLS 1.3 where possible. Ensure the certificate SAN includes the MX hostname (not just the apex domain). Publish MTA-STS to enforce TLS for inbound traffic and TLS-RPT to receive failure reports — both are zero-cost upgrades that meaningfully harden mail-in-transit security.