Setting up email for a new business domain is a set of small decisions that are awkward to change later: which addresses exist, whether they are mailboxes or forwarders, and who can send as them. Getting them right at the start costs an hour.
Create fewer addresses than you think
Every address is something to monitor, and an unmonitored address is worse than a missing one. A customer writes to it and hears nothing.
For most small businesses: one address per person who needs one, one general address, and one for billing if that is a different person.
Add role addresses when someone owns them, not in anticipation of growth. careers@ on a company with no vacancies is a mailbox nobody reads. For running the shared ones properly, see How to Set Up Shared and Role-Based Mailboxes.
Decide the naming convention once
First name, first initial and surname, or full name with a separator. Any of them works; mixing them does not.
A domain with jane@, j.smith@ and janesmith@ is one where nobody can guess a colleague's address, and where a customer writing to the obvious form gets a bounce.
Pick one, write it down, and apply it to everyone including the people who join later.
Mailbox or forwarder
A mailbox stores mail on the server and counts against your disk. A forwarder sends it to an existing mailbox and uses no space.
Use mailboxes for people. Use forwarders for role addresses handled by one person. It avoids a second password and a second inbox to check.
The catch with forwarding to an external provider: the mail leaves your server carrying the original sender's address, which fails their authentication check and is attributed to you. Fine at low volume, a reputation problem on a busy address. Understanding SPF, DKIM and DMARC Records has the detail.
Set a quota on every mailbox
Not because anyone will hit it, but because unlimited means the mailbox is limited by the whole account instead.
One mailbox nobody has emptied in eight years can consume the disk the website needs, and the failure appears as a site that cannot write files, which nobody connects to email. Managing Mailbox Quotas and Email Disk Usage walks through what actually fills them.
2 GB is a reasonable default. Adjust upward for people who need it instead of starting from no limit.
Turn the catch-all off
A catch-all accepts mail to every address at the domain, including the thousands of guessed addresses automated senders try.
It is the usual reason a mailbox nobody uses becomes the largest thing on an account, and it hides your own typos indefinitely, mail to a misspelled address arrives, so nobody notices the misspelling.
Create the addresses you use and let the rest bounce.
Publish SPF from day one
One TXT record listing what may send mail for the domain.
Without it your mail is unverified from the first message, and sending reputation is far easier to build than to repair. Add DKIM at the same time if your host supports it: most do, and it is a switch in place of a project.
One rule: exactly one SPF record. Adding a second when you add a sending service makes both invalid, which is worse than having none.
Decide where mail lives
Two arrangements, and the choice affects everything else.
On your hosting account: included, simple, and shares the server's sending reputation with other accounts.
With an external provider. A subscription, better collaboration tools, and independent of your hosting.
If you choose external, there is one setting people miss: the hosting account must be told not to deliver mail for the domain locally, or messages your own website sends to your own domain never leave the server. How to Use an External Mail Provider with Your Domain goes into it.
Use IMAP, and set up devices properly
IMAP keeps mail on the server, so every device shows the same thing and the mail is included in the server's backups.
POP downloads to one device, where it is protected by whatever backs up that laptop, which for most people is nothing. For the difference, see IMAP vs POP: Which Should You Use.
Give people the settings in writing when you create their account: server, ports, encryption, and the reminder that the username is the full address instead of the part before the @.
The website's mail is separate
Creating mailboxes does not change how your site sends contact form messages or order confirmations.
Configure the site to authenticate to a real mailbox over SMTP, so everything from your domain comes from one authorised place. A site handing mail to the server's default program is the most common reason form notifications quietly stop arriving. How to Fix WordPress Email Not Sending picks it up from there.
Test before anyone relies on it
Send to each new address from outside, and from each address to an external one. Then read the received headers and confirm authentication passed.
A message that arrived is not the same as a message that authenticated, and the difference appears weeks later as mail drifting into spam folders.
A brand-new domain has no reputation at all, which changes how the first weeks of sending should look. How to Warm Up a New Sending Domain has the detail.
Test delivery in both directions before announcing it
A new business domain is announced to customers, and the announcement is the first real test of the mail configuration. Send from the new address to an external account and reply back, then check where each message landed rather than only whether it arrived. Mail delivered to a spam folder has technically worked and practically has not, and the cause is usually a record that was not published before the first message was sent. Doing this before anybody is told means the correction is a configuration change rather than a reputation to repair.