Экстрагируем сертификат:

openssl pkcs12 -in [yourfile.pfx] -clcerts -nokeys -out [certificate.crt]

Получаем RSA ключ с паролем

openssl pkcs12 -in [yourfile.pfx] -nocerts -out [keyfile-encrypted.key]

Получаем RSA ключ без пароля:

openssl rsa -in [keyfile-encrypted.key] -out [keyfile-decrypted.key]

Получаем PEM ключ:

openssl rsa -in [keyfile-encrypted.key] -outform PEM -out [keyfile-encrypted-pem.key]

 openssl s_client -connect [ip-or-host]:25 -CAfile CA-cert.pem -starttls smtp | openssl x509 -enddate -noout