Communication just looks more professional coming from your own domain
Most people have requested or received a free email address at some point. At Hotmail for example. Or Gmail. Or at one of the hundreds of other providers. Which is perfectly fine for most people, but not for business owners.
What’s wrong with my email address?
An email address consists of 2 parts: the name of it’s owner and the name of the domain on which the email address is registered. This domain is always a business name or a brand and therefore strongly associated with a company. So everything you use that email address to communicate with somebody, you’re in effect advertising a business that is not your own.
Additionally, people almost expect an email address to end with gmail.com or hotmail.com. Seeing it end with something else (read: you company domain) makes it fascinating. For some people their curiosity will even make them add that last part into their web browser (e.g. Internet Explorer, Mozilla Firefoz or Google Chrome) resulting in your website being displayed!
Your email address gives everybody access to your website
An example: John’s Bakery is a bakery owned by John. John knows that if he wants his business to remain sustainable, he needs to have a web presence. So one morning he decides to get a website and the domain www.johnsbakery.com.
For his email communication he was using Gmail: firstname.lastname@example.org but with his new domain he decides to change that to email@example.com. That does look a lot better, doesn’t it?