Mosquitto starts to support OCSP stapling since version 1.6(20190417). Online Certificate Status Protocol(OCSP) can be used to query a certicate from client to server whether it is still valid or be revoked.

OCSP is an alternative way for Certificate Revoke List(CRL). One of pros of OCSP is no need to maintain large list same as CRL. Most part of cons is that few programs support it. Some well-known programs such as Apache and Nginx support it. Common between OCSP and CRL is that it’s need to periodiocally update content to be queried by clients.  

Reference: -Mosquitto CHANGELOG.txt