Are you using the webmail interface or an App. If the latter which one? It seems your outgoing Mail server is not working. See this link for more info: https://www.telus.com/en/bc/support/topic/gmail/getting-started?INTCMP=Tcom_supporthome_to_email
I don't know about Telus, but this happens to me in the gmail app and always has, with every device, on every kind of service, since apps began and probably even before that; tried all the fixes, nothing fixes. 😣 So... any help with gmail?