The message means that the SMTP server must have the same email address as the one in your FROM line in the email message. Many email providers are getting tight on security and that is one of the tests to prevent spam. This usually happens when a person has several email accounts, yet uses the same SMTP server for all of them. You can fix this by going to account settings pane and scrolling down left side until you see 'Outgoing Servers SMTP' and then list the entries. There must be one for each email account and each one must have a matching email id to the account. You should also check to see if you are using any authentication such as password. For example, if you have three gmail accounts, you need three gmail SMTP servers, one for each email address. A simple way to keep track of them is to fill in the 'Description' field with unique indentifier for each one. Then, when looking at account settings pane, it will be easy to verify that you have set the right smtp server.

Okay there are multiple road runner emails configured with my ISP, but I only have my email address (wheeler@wi.rr.com) configured in Thunderbird on my computer. The FROM line is wheeler@wi.rr.com and the SMTP server is Smtp-server.wi.rr.com and the user name, when you click on edit under SMTP server, is wheeler. There isn't anywhere to enter an email address under the edit menu. When I click on account settings Outgoing Servers SMTP' there isn't a list of anything. It just lists default. My wife is getting the same error message when she tries to send emails on her computer. Her computer, like mine, only has her email address configured in Thunderbird. I see under SMTP server there is a button that says "add". I can add the other email addresses, but I do not know how to add additional SMTP servers. Thanks! Eric

The user name needs to be wheeler@wi.rr.com, not wheeler. You do not need to add another smtp server if your Thunderbird only has one email account. You need to have one smtp server for each account.

I did what you said and it worked!! Thanks for all your help!

You're very welcome.