Right click the account in the left column and select Settings.

Change the name in the YOUR NAME field.

Where is the account? What left column? I have no columns.

Ok, I found the column and went to settings; however, my name is listed there as Mary Smith: my husband's name is not listed at all and it doesn't show I'm listed as Mary Doe.

This is why it is so hard to troubleshoot problems in the Internet especially with no details.

When you are looking at the main window do you see the Folder Pane down the left side of the window with your email accounts listed? If not press the alt key to make the menu bar appear and select View-Layout-Folder Pane.

Now follow the original instructions.

All this is assuming that you and your husband have separate accounts. If you are sharing the same account then forget it. There is only one name associated with an email account. Then the answer is get a second account in your name.

Then you are using the SMTP server for your husbands account. Thunderbird is good but it cannot pick Mary Doe out of midair.

Go back to account settings. Go to the very bottom of the account listing on the left and select Outgoing Server (SMTP).

Is there an account for you and and an account for your husband? If not make it that way and associate the correct outgoing server to the correct account. Make sure to name it accordingly so you will know the difference.

Well now I am confused. You marked it solved but I am not sure if you figured it out by your last posting.