I've had some reject my e-mail address because it contains their company name. REI was one (ie it wouldn't allow rei@domain.com but would accept reicoop@domain.com)
I had my account marked as suspicious and closed in a financial institution for this a few years ago. They were concerned I was a bad actor attempting to impersonate an employee. It was very annoying, because no one from customer support could talk to me directly, it had to flow through legal. Very stupid.
I have since stopped doing this out of fear that it will actually cause me more headaches with people/systems that don't understand how email works.
I was just able to create an account using `rei@<mydomain>` on rei.com w/o any issues. Now, figuring out how to delete the account is another matter entirely...
Cool, they probably changed it, this was years ago. I've had similar issues with other companies, REI is just the only one I can I really recall right now.
I haven't had an outright rejection, but definitely a few odd moments with call center agents. "theircompanyname@myname.com" is definitely not the default expectation :)
I have since stopped doing this out of fear that it will actually cause me more headaches with people/systems that don't understand how email works.