When someone sends you email, it goes to your email server. Much like a physical home, your email server has an address that makes sure email finds it. This is called an MX record.
How does an MX record look?
MX records look like this:
Where do I find my MX record?
Whoever hosts your email will have a record of this. You may be able to login to your control panel with them or contact them directly to find out.