If you get an error message, similar to the one below, when attempting to send mail messages from thunderbird:

Then please check to see if your outgoing settings look something like this in Thunderbird:

The important part here is that you have either the 'TLS' or 'SSL' options checked.

The 'Use name and password' option is only required when outside the Chemistry Departments Network.

Either one should work. These two options are to ensure that your password is encrypted when connecting to the chemistry mail server.