Suddenly we are unable to send email from all of our Thunderbird accounts, but they still receive email. Our provider is Spectrum. We can send email if we log in directly to the Spectrum email server. I've tried turning off Webroot and Microsoft security settings, but still cannot send. I don't know what else to try. The person at Spectrum said it was not on their end. He suggested removing and then reinstalling a Thunderbird email account, but I'm reluctant to try this for fear of losing email in Thunderbird or not being able to reinstall the account. I don't know how to take or send screenshots so here is a copy of the error message that pops up in Thunderbird: Sending of the message failed. An error occurred while sending mail. The mail server responded: <[email protected]> sender rejected. The email address you are sending as must match the email address you used to auth. Please check your SMTP settings. AUP#Out-1500. Please verify that your email address is correct in your account settings and try again. Thanks for any help you can give me. Ed Bender ([email protected])