I am unable to send emails externally, as they always come back with an error message saying "relaying denied. IP name possibly forged."
I have never had this issue before, and the recipient of the email is definitely not forged.
Thanks for raising this with us.
Since you are able to send out emails using your phone, then there's no issues within the Email server.
Try to change the password of your Email account and update it in outlook as it may resolve the issue.