Let’s Begin:
This works if you already have an expired letsencrypt ssl certificate and assuming you have already deployed SSL in you zimbra system. However, if you come up here already, and would like to know how to setup letsencrypt on your system you may read my other article here:
https://tweenpath.net/installing-encrypt-zimbra-server/
Log on Zimbra user then stop proxy and mail box service for renew proccess.
su zimbra zmproxyctl stop zmmailboxdctl stop
Then return root user and renew Letsencrypt certificate
exit
letsencrypt renew: Change directory to Zimbra Letsecnrpyt SSL folder
