I had the same problem. The answer may seem strange. Telus gives you a username like “a0Pi6T4A” this is the name of your mailbox. Than you choose your aliases, they are email addresses that are like just there to forward the mail to your main mailbox(you can have several of those pointing to same mailbox). Something like hello@telus.net.

When prompted for your username and password you can either type your username “a0Pi6T4A” or your alias including @telus.net and it will work.

You are right that information is nowhere I could find on their site. I called their tech support, all telecom companies have 24hour tech support.

As for mac mail… I was with Bell back than and the problem is mail 3 or 4 I cant remember which one, it wasnt selecting the right port by default even is the software said it was selecting the right port(110 for pop, 143 for imap and 25 for smtp). The fix was simply to change the port manually.