Me: That’s because your domain gives you a location on the internet to accept email.
Customer: But we have Telecom broadband, which provides our internet! So what does our domain do? What is that for?
Me:Okay. I'll try to use a real life parable here. Telecom builds roads to access the internet. You can use them to browse websites, etc.
Me:Now, your domain name is like your house, and the web mail is your mailbox so that mail can be delivered to your online address. By cancelling payment for your domain, you basically just sold your house.