Don't the ISP mail servers need to have SMTP relay available for you to basically relay the message into their system from externally? I don't think they will allow that. It makes it super easy for spammers to spoof and take advantage of their system.
You could find the IMAP & POP3 settings for each email and add them into Outlook. IE for Shawmail:
https://community.shaw.ca/docs/DOC-5375