I have tried qdoxsxerox\firstname.lastname@example.org and qdoxsxerox.com\email@example.com. Previously, I have tried \\qdoxsxerox.com\firstname.lastname@example.org, based on an older post. I have pretty much tried every combination I can think of.
Thank you for the additional information.
It does look like you have tried all of the main UserID combinations. I have noticed that the SharePoint URL you have shared is a little different compared to the ones that I've typically seen. I am going to pass along this information to a couple additional folks here and have them take a look.
In the meantime, would you mind giving one more UserID combination a try? Could you please try qdoxs\email@example.com and let me know the outcome?