Here is the complete message: An error occurred while sending mail. The mail server responded: 5.7.1 [address] Relay access denied. Please check the message recipient [address] and try again Using Outlook with same server settings, messages go through. If I resend multiple times from Thunderbird the message goes through. If I move the message to draft, and then check the isp's webmail, the message has been received by my isp and is in the proper webmail draft folder. Last night I had the same issues on my home computer (I'm currently at work). Any help?