I was sent my regular email from Shaw Support Community and had a look at what people are asking about. I saw that there was an email set up for different email providers. I use Outlook 2007 and it said in Outgoing to uncheck require authentication.
Well mine was checked so I unchecked my 3 email accounts.
Well they all stopped working for outgoing. I went back and checked the Outgoing server requires authentication and all is well again.,
I suggest you change the post at Email Client: Send/Receive Troubleshooting
It said to uncheck for 2007 Outlook,