Mail with no website.
THE SITUATION
A business with professional email on their domain and no website, or a website elsewhere.
WHAT IS NEEDED
MX records pointing at the mail server An A record for the mail hostname SPF and DKIM A DMARC record
WHAT IS NOT NEEDED
An A record for the domain, unless you want it to resolve.
WHAT TO DO WITH THE BARE DOMAIN
Point it somewhere. A holding page, or a redirect to their social presence.
A business email address on a domain that shows nothing when visited looks odd to anyone who checks.
THE PRACTICAL SETUP
A small hosting account used only for mailboxes, with a simple holding page.
WHAT TO CONFIGURE PROPERLY
SPF and DKIM. Email-only domains suffer the same deliverability problems as any other, and getting authentication right at setup prevents most of them.
MAIL ROUTING
If mail is on the hosting, local routing is correct.
If it is elsewhere, set routing to remote.
WHEN THEY LATER WANT A WEBSITE
Add an A record and build it. Mail is unaffected.