> /usr/local/bin/openssl s_client -showcerts -connect ...:25 -starttls smtp
CONNECTED(00000003)
depth=2 C = US, O = GeoTrust Inc., CN = GeoTrust Global CA
verify error:num=20:unable to get local issuer certificate
verify return:0
---
Certificate chain
0 s:/OU=...
i:/C=US/O=GeoTrust Inc./CN=RapidSSL SHA256 CA - G3
-----BEGIN CERTIFICATE-----
...
-----END CERTIFICATE-----
1 s:/C=US/O=GeoTrust Inc./CN=RapidSSL SHA256 CA - G3
i:/C=US/O=GeoTrust Inc./CN=GeoTrust Global CA
-----BEGIN CERTIFICATE-----
MIIEJTCCAw2gAwIBAgIDAjp3MA0GCSqGSIb3DQEBCwUAMEIxCzAJBgNVBAYTAlVT
...
gP8L8mJMcCaY
-----END CERTIFICATE-----
2 s:/C=US/O=GeoTrust Inc./CN=GeoTrust Global CA
i:/C=US/O=Equifax/OU=Equifax Secure Certificate Authority
-----BEGIN CERTIFICATE-----
MIIDfTCCAuagAwIBAgIDErvmMA0GCSqGSIb3DQEBBQUAME4xCzAJBgNVBAYTAlVT
...
b8ravHNjkOR/ez4iyz0H7V84dJzjA1BOoa+Y7mHyhD8S
-----END CERTIFICATE-----