Hi Saurav •,
Welcome to Microsoft Q&A forum.
As I understand, you want to know about the certificate email received for Azure Database for PostgreSQL Flexible Server.
For .NET (Npgsql) users on Windows, connecting to Azure Database for PostgreSQL - Flexible Servers deployed in Azure Government cloud regions (US Gov Virginia, US Gov Texas, US Gov Arizona) make sure both Microsoft RSA Root Certificate Authority 2017 and DigiCert Global Root G2 both exist in Windows Certificate Store, Trusted Root Certification Authorities. If any certificates don't exist, import the missing certificate.
For .NET (Npgsql) users on Windows, connecting to Azure Database for PostgreSQL - Flexible Servers deployed in Azure public regions worldwide make sure both Microsoft RSA Root Certificate Authority 2017 and DigiCert Global Root CA both exist in Windows Certificate Store, Trusted Root Certification Authorities. If any certificates don't exist, import the missing certificate.
Here is the complete MS documentation for the same:
Hope this helps. Let us know if you have more queries.
Thanks