Getting this message below when sending emails, but other times it works fine.

There have been major problems with Spectrum/Charter/TWC/Roadrunner lately. Neither mail.twc.com (TWC's email servers) or mobile.charter.net (Spectrum and Charter's servers) appear to be online right now and may have been down for some time. From what we hear from their users, service has been intermittent for a while but it's gotten worse in the past few weeks. It is not specifically a Thunderbird issue - it appears to affect most or all 3rd-party email clients, including Outlook, eMClient, etc. Webmail still works. Spectrum's support usually (but not always!) don't admit to any problems, only saying that they only support webmail. Here's a link to Spectrum's own user forum where you can see many discussions of the situation: https://community.spectrum.net/categories/email-22 If you have time, you could contact Spectrum for status.