EnterraHost
A mailbox is an address at your own domain, so [email protected] rather than a free inbox you do not control. Creating the first one is an order rather than a signup. You choose how much storage it gets and which tier it sits on, and the address itself is made once the order is paid.
If you have not registered the domain yet, do that first. A mailbox needs a domain to live on, and registering a domain is its own short job.
Pick the tier before the size
There are two tiers, Lite and Pro, and both come in the same two sizes. That is the part worth understanding before you click, because it means storage is not how you choose the tier.
Lite is mail, calendar and contacts. Pro adds the things a team tends to need later. Calendar and contacts that sync to a phone through the standard protocols rather than mail alone, the ability to open and edit documents inside the webmail, every mailbox on the domain in one login, and a longer archive. The full breakdown is on the business email page.
If you are buying for one person who reads mail in a desktop client, Lite is the honest answer. If you are buying for a small team, or you want your phone's calendar and contacts to follow the mailbox, that is what Pro is for.
Then pick the size
A mailbox comes as 10 GB or 50 GB, and both sizes are available on both tiers. Most single users never fill 10 GB, because modern mail is small once attachments are stripped out. Choose 50 GB when the mailbox carries years of history, or when attachments genuinely live in it.
You can add more later without rebuilding anything — storage is added in blocks and added to a mailbox whenever you need it.
What the order actually asks for
The order form wants the domain the mailbox belongs to, how many mailboxes of each tier and size you want, and the billing term. You can mix them, so two Lite mailboxes and one Pro mailbox is a normal order rather than three separate ones.
Nothing is created at that point. The order is a request, and the mailbox is built when the order is paid, and the address itself is chosen after that.
Choosing the address
The part people expect to happen at checkout happens afterwards. Once the service is live you log in to the toolbox, open the email service, and add the address you want — the part before the @ is yours to pick, and the domain is already fixed.
That is also where aliases and catch-alls live, which is a different job from creating a mailbox and is covered in creating an alias or a catch-all.
If you already have mail somewhere else
You do not have to choose between running both or losing your history. Mail, calendar and contacts are copied across for you at no cost, and moving your existing mail across covers what is copied and what is not.