When a domain name represents your company branding, rather than an online service like Hotmail, Yahoo, Google, Comcast, or Microsoft Online, it is a custom domain. An email address like <your name>@<your business> projects a professional image and helps to imprint your brand with customers and the public. Every email you send reinforces the message that you have a unique identity and are not just using a public email service. Like your company logo, your custom domain helps set you apart from other businesses.

To use a custom domain with Microsoft Office 365, you must first own the domain name that you want to use. If you do not already have a domain, they are simple and inexpensive to acquire from a domain name registrar. Domain names must be unique, so be prepared to be a little flexible. If someone already owns the rights to your first choice, you might need to try a variation or two. Services and pricing vary widely, but you can buy a domain name, which you must renew annually for about $5–$20.