After updating to TB 115.5.2, we keep getting the following error message when we try to send or forward an email: Sending of the message failed. An error occurred while sending mail. The server is not responded. No such domain at this location. Please check message recipient "xxxxx@gmail.com" and try again. I get this error on all emails we try to send. We get this same error on my spouse's computer also that we use Thunderbird with. I have already checked settings with my ISP and the POP settings are correct. We can use other mail servers such as outlook.com and gmail.com using Thunderbird. ISP is cis broadband. have checked firewall, have uninstalled Thunderbird and re-installed without solution to problem. ISP has checked port to make sure it is not blocked. incoming emails do not seem to be effected. gmcfie@cis-broadband.com