Hello,
You should make sure that CS-Cart 2.x core and necessary add-ons don't have hardcoded constants on curl_setopt calls, forcing to use SSLv3 instead of TLS 1.x. Also you should check the version of cURL PHP extension and how it was compiled with OpenSSL (what version of OpenSSL do you use?). Ask your hosting provider to check it for you.
Sorry for the late reply. To date USPS is still working.
Well now you are getting beyond my knowledge. Can you give me more explicit instruction on what to check.
David DeWitt