Hi, I wanted to use the Thunderbird. Could You please tell me that using thunderbird is secure and wont have any of the issues with Security and Privacy ..???

Thunderbird is as secure as we can make it, but no email is secure, only sort of secure. That goes especially for the web mail providers and is inherent in the unencrypted transmission of the email body. Thunderbird does not contain trackers or phone home your personal information if that is what your are trying to ascertain.