Letsencrypt is one of the best free and automated SSL certificate issuing authority that makes it possible for almost anyone to get a free SSL certificate and install it on almost any website, application or server on demand. Letsencrypt is backed by some of the largest internet companies such as CISCO, SHOPIFY, FACEBOOK, REDHAT and has been deployed on more than 250 million website.  However letsencrypt certificates are valid for only 90 days and a renewal is required there after. This tutorial provides a guide on how to renew a letsencrypt SSL certificate installed on Zimbra Mail Server Open Source Edition OSE.