Thunderbird 15.0.1 cannot use Exchange 2003 SMTP

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http://serverfault.com – I'm having the strangest time getting a Thunderbird email client to connect to my Exchange 2003 server. I got the incoming IMAP account set up no problem, and I can receive mail. However sending mail will not work no matter what SMTP settings I enter. After checking the server, the proper settings should be port 25 with no authentication or connection security, which I have entered. I can ping the hostname of the server from the client machine in question. The Thunderbird error message I get is: "Sending of message failed. The message could not be sent because the connection to SMTP ser (HowTos)