To view certificate details
openssl x509 -text -noout -in SSL_FILE.crt
For web server
openssl s_client -showcerts -connect serverok.in:443
Or
curl -vI https://serverok.in
IMAP via SSL
openssl s_client -showcerts -connect mail.yourdomain.com:993 -servername mail.yourdomain.com
POP3 via SSL
openssl s_client -showcerts -connect mail.example.com:995 -servername mail.yourdomain.com
SMTP via SSL
openssl s_client -showcerts -connect mail.yourdomain.com:465 -servername mail.yourdomain.com
SMTP via TLS/StartTLS
openssl s_client -starttls smtp -showcerts -connect mail.yourdomain.com:25 -servername mail.yourdomain.com