What is a sending subdomain, and why use one?

A sending subdomain is a subdomain specifically configured for sending email, such as mail.yourdomain.com or em.yourdomain.com. Rather than sending directly from your root domain, you route email through this dedicated subdomain.

Primary reasons: it protects your root domain from reputation damage. If email reputation suffers, it affects only the subdomain; your main domain's web presence and corporate email remain unaffected. It also enables clean DNS configuration without cluttering your root domain's records.

Authentication setup becomes cleaner with subdomains. You can delegate DKIM signing and SPF to the subdomain without modifying records on your root domain, which may have stricter change control processes.

Build your docks on a separate pier. Shipping activity stays organized, and any incidents at the docks don't threaten the main harbor.