1. port 25
• openssl s_client -starttls smtp -host g.pyon.org -port 25
2. port 587
mail submission port
$ openssl s_client -host smtp.gmail.com -port 587 -starttls smtp Connecting to 142.251.170.109 CONNECTED(00000003) depth=2 C=US, O=Google Trust Services LLC, CN=GTS Root R1 verify error:num=20:unable to get local issuer certificate verify return:1 depth=1 C=US, O=Google Trust Services LLC, CN=GTS CA 1C3 verify return:1 depth=0 CN=smtp.gmail.com verify return:1 --- Certificate chain 0 s:CN=smtp.gmail.com i:C=US, O=Google Trust Services LLC, CN=GTS CA 1C3 a:PKEY: id-ecPublicKey, 256 (bit); sigalg: RSA-SHA256 v:NotBefore: Nov 20 08:09:17 2023 GMT; NotAfter: Feb 12 08:09:16 2024 GMT 1 s:C=US, O=Google Trust Services LLC, CN=GTS CA 1C3 i:C=US, O=Google Trust Services LLC, CN=GTS Root R1 a:PKEY: rsaEncryption, 2048 (bit); sigalg: RSA-SHA256 v:NotBefore: Aug 13 00:00:42 2020 GMT; NotAfter: Sep 30 00:00:42 2027 GMT 2 s:C=US, O=Google Trust Services LLC, CN=GTS Root R1 i:C=BE, O=GlobalSign nv-sa, OU=Root CA, CN=GlobalSign Root CA a:PKEY: rsaEncryption, 4096 (bit); sigalg: RSA-SHA256 v:NotBefore: Jun 19 00:00:42 2020 GMT; NotAfter: Jan 28 00:00:42 2028 GMT --- Server certificate -----BEGIN CERTIFICATE----- MIIEiTCCA3GgAwIBAgIRAIByTLUXdgC8CYgIU91G50AwDQYJKoZIhvcNAQELBQAw RjELMAkGA1UEBhMCVVMxIjAgBgNVBAoTGUdvb2dsZSBUcnVzdCBTZXJ2aWNlcyBM TEMxEzARBgNVBAMTCkdUUyBDQSAxQzMwHhcNMjMxMTIwMDgwOTE3WhcNMjQwMjEy MDgwOTE2WjAZMRcwFQYDVQQDEw5zbXRwLmdtYWlsLmNvbTBZMBMGByqGSM49AgEG CCqGSM49AwEHA0IABEPmeIvl4U3Lbi4mQubURTvQIXrUiTerW1j9nexhcuz9KpJ2 rt34EtbFPbuDfYWVC2zji9a+SFYRU75+any1u+WjggJoMIICZDAOBgNVHQ8BAf8E BAMCB4AwEwYDVR0lBAwwCgYIKwYBBQUHAwEwDAYDVR0TAQH/BAIwADAdBgNVHQ4E FgQU+kJhZ6EEaBvaTH1xOfjC3qdxzC0wHwYDVR0jBBgwFoAUinR/r4XN7pXNPZzQ 4kYU83E1HScwagYIKwYBBQUHAQEEXjBcMCcGCCsGAQUFBzABhhtodHRwOi8vb2Nz cC5wa2kuZ29vZy9ndHMxYzMwMQYIKwYBBQUHMAKGJWh0dHA6Ly9wa2kuZ29vZy9y ZXBvL2NlcnRzL2d0czFjMy5kZXIwGQYDVR0RBBIwEIIOc210cC5nbWFpbC5jb20w IQYDVR0gBBowGDAIBgZngQwBAgEwDAYKKwYBBAHWeQIFAzA8BgNVHR8ENTAzMDGg L6AthitodHRwOi8vY3Jscy5wa2kuZ29vZy9ndHMxYzMvUU92SjBOMXNUMkEuY3Js MIIBBQYKKwYBBAHWeQIEAgSB9gSB8wDxAHcAdv+IPwq2+5VRwmHM9Ye6NLSkzbsp 3GhCCp/mZ0xaOnQAAAGL6/3F3QAABAMASDBGAiEA+OenGg6Oa/xgFbfFPQvExWk+ l96Py1QItoMES0yz5e0CIQCqkVkWlmtA13X21+R/mIRcT+2yTpWxA0aZay6ONkgI UwB2AEiw42vapkc0D+VqAvqdMOscUgHLVt0sgdm7v6s52IRzAAABi+v9xdMAAAQD AEcwRQIgc9kRv0ZEMNgoytEgojAcBJnUnUIf2WOqJGMM+3jj+xECIQCKYoAjexAo KeZaX/g0yY0JJUvW7J4Dcqm5QxsE4c8HfjANBgkqhkiG9w0BAQsFAAOCAQEAWqjp hSDNzPY7y2UubkGnXN2x0vi7PLevugt17vfstIe7zWRhC6jNX0k6OKAKhPdsgjhB npxD6CKgw2XZSBOWOHexF68E6LSQNtrOSR736QrG5UgGJAuTHCwKkKLAr8RNbKJv /USDxln3ol9Uzh2vLFRbov/7+k+EmYsxY1yxViM4XnluU1ikB9SfmJlREwv+2wVx c/jgDa964ZYhG4ziQ/SpK4sDg73u8sUvwLweykcfSgtHED9F3LCqsDpmcin04A5Q 3WONmT7LZEO4MtzR+nXAW+CHvp6JWQ7u8cYOGBKodf7FYp4tq6jTd9MsTKXTXGPb GnGnrQiLbu2THZKvKg== -----END CERTIFICATE----- subject=CN=smtp.gmail.com issuer=C=US, O=Google Trust Services LLC, CN=GTS CA 1C3 --- No client certificate CA names sent Peer signing digest: SHA256 Peer signature type: ECDSA Server Temp Key: X25519, 253 bits --- SSL handshake has read 4581 bytes and written 435 bytes Verification error: unable to get local issuer certificate --- New, TLSv1.3, Cipher is TLS_AES_256_GCM_SHA384 Server public key is 256 bit This TLS version forbids renegotiation. Compression: NONE Expansion: NONE No ALPN negotiated Early data was not sent Verify return code: 20 (unable to get local issuer certificate) --- 250 SMTPUTF8