I also can't think of any reason to use a Public Mobile SMTP server. Public Mobile isn't an internet provider, and doesn't issue e-mail addresses to subscribers. Any use of Public Mobile or Telus's servers for e-mail purposes with be unauthorized and otherwise something that you're not supposed to do. You would be using someone else's/another company's e-mail servers to relay/redirect your e-mail message communications. Even the outgoing messages did go through, such relaying would likely fail e-mail security checks and get flagged as spoofing, unsafe, or as spam.
There was a day that even some of Canada's largest ISPs allowed such a security vulnerability. It was easy to spoof yourself as being someone else, and then even use the proper servers to send the messages, making the spoofed messages appear more legitimate. I tried that before as a joke to a friend (example: making it look like friends were sending messages to themselves, etc.).
