Uninstalling and reinstalling Thunderbird only installs the program it has no effect on your mail accounts. The password you use for each mail account is the same password you use to access that webmail account using a browser. So in TB usually the password used to Get Messages is the same as the one used to Send messages for that mail account. Try the following on one computer: Tools > Options > Security > Passwords tab * click on 'Saved Passwords' * click on 'show passwords' * Select the 'smtp:// mail account password for problem account' * click on 'Remove' * click on 'Close' * click on 'OK to save changes to Options. * Close Thunderbird. * Wait a few moments for background processing to complete. * Restart Thunderbird. * Try to send an email. * At the prompt, Type in correct password and select the option for Password Manager to remember the password. * click on OK What happened? If this fixed the issue - great. If not, what error message did you get....word for word? Then please supply some info: '''Q1. '''You have four computers - do you have the same email address on each computer or do you have different email addresses on each computer? '''Q2'''. Are the accounts on all of the computers, all the same type eg: POP or IMAP? What type? '''Q3. ''' On the computer which you just removed the smtp password and re-entered it..if still a problem then supply this info. Tools > Account Settings > Outgoing Server (SMTP) How many outgoing servers are listed? '''Q4. ''' In Thunderbird - using the same computer * Tools > Troubleshooting Information * do not select 'include account name' * click on 'Copy text to clipboard' * paste the info into this forum's reply box. * you can remove all info on fonts and printers but nothing else.