The domain is @telusplanet.net
(Yes, he is old school.)
I think I found the solution.
Outgoing Mail (SMTP) Server: smtp.gmail.com
Use Authentication: Yes
Use Secure Connection: Yes (this can be TLS or SSL depending on your mail client)
Username: your GMail account, i.e.
user@gmail.com
Password: your GMail password
Port: 465 or 587
That brings me back to sending as my @gmail.com address.
Then go into your Gmail and do the following:
1.On your computer, open Gmail.
2.In the top right, click Settings Settings and then Settings.(sic)
3.Click the Accounts and Import or Accounts tab.
4.In the "Send mail as" section, click Add another email address you own.
5.Enter your name and the address you want to send from.
6.Click Next Step.
7.Enter the SMTP server (for example, smtp.domain.com) and the username and password on that account.
8.Click Add account.
I just tested it and it seems to work as I wanted. Yes, I am fully aware of spoofing; which is why I didn't mind doing the authenticating. I just knew there had to be a way.
Sources:
https://www.siteground.com/kb/google_free_smtp_server/
https://support.google.com/a/answer/22370?hl=en