This directory is supposed to have 3 keys which are copied to various places to mailserver.
 
 - ca.crt
   Certification authority public keys (or "intermediate certificate"). There is 
   "-----BEGIN CERTIFICATE-----" once or more times.
   
 - server.crt
   Your public key generated by your CA. It should have one "-----BEGIN CERTIFICATE-----"
   in it
   
 - server.key
   Your private key, it should have "-----BEGIN RSA PRIVATE KEY-----" in it


There is also
 - dh1024.pem
   Its generated Diffie-Hellman paramaters. File is generated once at first container startup - there is no need to manipulate with that file even if you changing all certs.