hi @ramaagcp
You may want to rephrase you question
You actually haven’t obtained any certificates
There is a 3 part approach to this problem
A) Obtain certificates this forum can help with approaches etc (if you articulate your setup and how you plan to do this). If you don’t know then a general google of let’s encrypt + zimbra should give you a good starting point. Alternatively you can search zimbra on this forum as it has been discussed before
B) Review zimbra documentation on how to do SSL installs. https://www.digicert.com/csr-creation-ssl-installation-zimbra.htm
C) Review testing here: Tutorial - Testing Mail Protocols with SSL/TLS
Andrei