That is the policy of your mail provider, I suggest you approach them for a solution.

Thanks for the quick response! Two things: 1. The webmail of Charter works for outgoing mail. Having problem only with the Thunderbird email agent. 2. Had a chat session with Charter, was recommended to use a US VPN. Would this work with Thunderbird?

Thanks for the quick response! Two things: 1. The webmail of Charter works for outgoing mail. Having problem only with the Thunderbird email agent.

That is also your providers policy. They have never restricted sending mail from their web site.

2. Had a chat session with Charter, was recommended to use a US VPN. Would this work with Thunderbird?

I had someone on here a week or month ago that was in dallas and had exactly the same problem. It was not being in the US that was important, it was connecting to the internet using their service. Historically I think they had a mobile server that cell phones were supposed to use that did not implement the constraint. I have no idea if it still exists. or if it works. Being in Australia I don't even get to access most of their servers to look up solutions because they are so xenophobic. (At least I think they are)

Temporary solution: save all outgoing mail in Draft folder, and as needed, log into webmail, send out all mail in Draft. Relatively painless and quick solution.