Hello Pinaki,
port 25 for smtp.gmail.com is not supported anymore. You have to use 465 for SSL or 587 for TLS.
For both cases you have to change also Transport Security Setting from "None" to "SSL/TLS".
Depending on your account setup the trust store configuration can be necessary too.
What also has to be checked is, if your HANA system can connect on network level to the SMTP server (maybe e.g. some firewall settings do not allow that).
If your system is behind a proxy, you also have to specify the proxy information in the HANA SMTP configuration.
Best Regards,
Florian