How can an affected user recover from such an attack?

Report all received emails as spam, add a filter to get rid of the @domain.com emails, and probably add the entire service to the blacklist so it doesn't happen again. Probably get rid of any paid account on that service one might have laying around.

If the email is targeted at a domain using mail servers from any major email provider (Gmail, Outlook), the user will probably find most emails into their spam folder anyway and the sending domain will get added to the spam list automatically. Especially if the attack hits multiple users on the same email service.