I upgraded my LPL email client to Thunderbird 3.0 and now cannot send mail. How do I fix this?

Thunderbird 3.0 is known to incorrectly modify existing secure outgoing mail settings the first time one sends a message. 
To fix this problem after upgrading, perform the following steps:

  • Start Thunderbird 3.0.
  • Click Write.
  • Compose a test message to yourself.
  • Click Send. If this fails, fix the problem as follows.
  • Click Tools -> "Account Settings" -> "Outgoing Server".
  • Click Edit.
  • In the "Server Name:" field, type hindmost.lpl.arizona.edu
  • In the "Port:" field, change 25 to 587.
  • Check the box next to "Use name and password".
  • Type your LPL username in the "User Name:" field.
  • Do not check the box next to "Use secure authentication" (uncheck it).
  • In the list next to "Connection security:", select "STARTTLS".
  • Click OK.
  • Click OK.

Brief Explanation:

While a mail server may allow either secure connection (STARTTLS) or secure authentication, 
a mail server may not support both methods at the same time.

The Thunderbird 3.0 upgrade process modifies your existing settings to try to use both methods, which will not work. 
The above procedure configures your email client to use secure connection only, which the LPL mail server supports.