What should I do if a website doesn’t accept an email alias?

Some websites won’t allow you to use an email alias, (I’m assuming by whitelisting domains). There may also be times when you may need to speak to customer service at a company, and it would be a hassle to give the rep an alias, because they just don’t know about them. How do I stay private on these websites without giving them my real email address, as I am definitely guilty of? Also, what are your experiences with customer service …

accept email email alias privacy website