Quote Originally Posted by bislewl View Post
Just wanted to post an update, the hosting provider confirmed the issue.

However they are saying it is the USPS server has banned the store's IP. But since USPS servers run multiple servers by forcing to use a server that hasn't banned that store it's working. They say they are contacting USPS to resolve the issue with being banned from that server.'

I'll update when I hear more
I thought I would update this late but still an update:

Hostgator responded with the following:
In attempt to have the block removed, I have reached out to the USPS abuse contact email provided in the network segment ownership information. Regrettably we do not have an eta on the matter, however as a quick workaround, your developer can change the local IP used for the cURL requests to XXX.XXX.XXX.XXX, which will show no issues when querying production.shippingapis.com directly no matter the IP it resolves to.

Further updates on the IP block will be provided as they become available, thank you for your patience.
about a month later they responded again with:

We have not received any response back from USPS however the connection shows to be working now:
Not sure what would cause an IP to be blacklisted by USPS...