After having trouble sending email with Thunderbird, I contacted Spectrum, a.k.a. Charter , support. It turns out, Spectrum will no longer connect with Thunderbird: "Thank you so much for your patience! I was doing some research and Spectrum is not allowing links with thunderbird server as of March 2024. You can use spectrum email on apple mail or outlook going forward but thunderbird email linking has been eliminated." Thought you would like to know. By the way, I'm using Linux (KUbuntu 22.04).