En aquel entonces era para puertos puramente SSL:
$ openssl s_client -showcerts -connect smtp.gmail.com:465 CONNECTED(00000003) depth=0 /C=US/ST=California/L=Mountain View/O=Google Inc/CN=smtp.gmail.com verify error:num=20:unable to get local issuer certificate verify return:1 depth=0 /C=US/ST=California/L=Mountain View/O=Google Inc/CN=smtp.gmail.com verify error:num=27:certificate not trusted verify return:1 depth=0 /C=US/ST=California/L=Mountain View/O=Google Inc/CN=smtp.gmail.com verify error:num=21:unable to verify the first certificate verify return:1 --- Certificate chain 0 s:/C=US/ST=California/L=Mountain View/O=Google Inc/CN=smtp.gmail.com i:/C=ZA/ST=Western Cape/L=Cape Town/O=Thawte Consulting cc/OU=Certification Services Division/CN=Thawte Premium Server CA/emailAddress=premium-server@thawte.com -----BEGIN CERTIFICATE----- MIIDVjCCAr+gAwIBAgIDP97OMA0GCSqGSIb3DQEBBAUAMIHOMQswCQYDVQQGEwJa QTEVMBMGA1UECBMMV2VzdGVybiBDYXBlMRIwEAYDVQQHEwlDYXBlIFRvd24xHTAb BgNVBAoTFFRoYXd0ZSBDb25zdWx0aW5nIGNjMSgwJgYDVQQLEx9DZXJ0aWZpY2F0 aW9uIFNlcnZpY2VzIERpdmlzaW9uMSEwHwYDVQQDExhUaGF3dGUgUHJlbWl1bSBT
Pero en algunos casos el puerto puede comenzar la sessión SSL a posteriori mediante el comando STARTTLS, en estos casos debemos especificar que protocolo debe hablar, por ejemplo:
$ openssl s_client -showcerts -connect smtp.gmail.com:25 -starttls smtp
CONNECTED(00000003)
depth=1 /C=US/O=Google Inc/CN=Google Internet Authority
verify error:num=20:unable to get local issuer certificate
verify return:0
---
Certificate chain
0 s:/C=US/ST=California/L=Mountain View/O=Google Inc/CN=smtp.gmail.com
i:/C=US/O=Google Inc/CN=Google Internet Authority
-----BEGIN CERTIFICATE-----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=
-----END CERTIFICATE-----
1 s:/C=US/O=Google Inc/CN=Google Internet Authority
i:/C=US/O=Equifax/OU=Equifax Secure Certificate Authority
-----BEGIN CERTIFICATE-----
MIICsDCCAhmgAwIBAgIDC2dxMA0GCSqGSIb3DQEBBQUAME4xCzAJBgNVBAYTAlVT
MRAwDgYDVQQKEwdFcXVpZmF4MS0wKwYDVQQLEyRFcXVpZmF4IFNlY3VyZSBDZXJ0
aWZpY2F0ZSBBdXRob3JpdHkwHhcNMDkwNjA4MjA0MzI3WhcNMTMwNjA3MTk0MzI3
WjBGMQswCQYDVQQGEwJVUzETMBEGA1UEChMKR29vZ2xlIEluYzEiMCAGA1UEAxMZ
R29vZ2xlIEludGVybmV0IEF1dGhvcml0eTCBnzANBgkqhkiG9w0BAQEFAAOBjQAw
gYkCgYEAye23pIucV+eEPkB9hPSP0XFjU5nneXQUr0SZMyCSjXvlKAy6rWxJfoNf
NFlOCnowzdDXxFdF7dWq1nMmzq0yE7jXDx07393cCDaob1FEm8rWIFJztyaHNWrb
qeXUWaUr/GcZOfqTGBhs3t0lig4zFEfC7wFQeeT9adGnwKziV28CAwEAAaOBozCB
oDAOBgNVHQ8BAf8EBAMCAQYwHQYDVR0OBBYEFL/AMOv1QxE+Z7qekfv8atrjaxIk
MB8GA1UdIwQYMBaAFEjmaPkr0rKV10fYIyAQTzOYkJ/UMBIGA1UdEwEB/wQIMAYB
Af8CAQAwOgYDVR0fBDMwMTAvoC2gK4YpaHR0cDovL2NybC5nZW90cnVzdC5jb20v
Y3Jscy9zZWN1cmVjYS5jcmwwDQYJKoZIhvcNAQEFBQADgYEAuIojxkiWsRF8YHde
BZqrocb6ghwYB8TrgbCoZutJqOkM0ymt9e8kTP3kS8p/XmOrmSfLnzYhLLkQYGfN
0rTw8Ktx5YtaiScRhKqOv5nwnQkhClIZmloJ0pC3+gz4fniisIWvXEyZ2VxVKfml
UUIuOss4jHg7y/j7lYe8vJD5UDI=
-----END CERTIFICATE-----
---
Server certificate
subject=/C=US/ST=California/L=Mountain View/O=Google Inc/CN=smtp.gmail.com
issuer=/C=US/O=Google Inc/CN=Google Internet Authority
---
No client certificate CA names sent
---
SSL handshake has read 1906 bytes and written 363 bytes
---
New, TLSv1/SSLv3, Cipher is RC4-SHA
Server public key is 1024 bit
Compression: NONE
Expansion: NONE
SSL-Session:
Protocol : TLSv1
Cipher : RC4-SHA
Session-ID: BA187E0D09C0CDDE4A3520D6991731686C09AF37EB4B5AA5DE6275B2ACB2A202
Session-ID-ctx:
Master-Key: 67579D9C448EFBC8C576EB29F76B3A89A80C7A43E67302B4A6A5205CA5E193F0DC127E205D08ED5BB3747749890110E4
Key-Arg : None
Start Time: 1304681288
Timeout : 300 (sec)
Verify return code: 20 (unable to get local issuer certificate)
---
250 ENHANCEDSTATUSCODES
