The Password Manager in Thunderbird should keep you logged in. Does Thunderbird not have a box to check in order to use the Password Manager?
Then YOU DO NOT have the proper password for the sympatico.ca mail serverSending of the message failed.
The message could not be sent using Outgoing server (SMTP) smtphm.sympatico.ca for an unknown reason.
Please verify that your Outgoing server (SMTP) settings are correct and try again.