In a business context an obfuscated email would give me pause.

Because they are making work for me.

Not helping me with my problem.

It's a tell for two scenarios. In the best case it suggests an intent to communicate "not for me" to me. More likely, there will be more hoops to jump through in the future. That's something I might want to avoid. I have the tee shirt.

the person I'm doing it for does not want to change the email provider nor create any email account/alias other than what they have now.

Ask them what they want, do what the want, cash the check. The solution is social, not technical. Good luck.