If you find you Mail Application not working properly subsequent to upgrading to OS X El Capitan, you need to make a few changes in the Preferences pane. To do this, while in the Mail App, choose Mail > Preferences > Accounts, then select your Telus account along the left margin. Once there, open the drop-down at Outgoing Mail Server, and select 'Edit SMTP Server list' and de-select 'Automatically detect and maintain account settings.
Your setup should look like this:
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