Subdomain delegation gives each third-party sender its own subdomain (for example news.example.com for the ESP, help.example.com for the helpdesk) with dedicated SPF, DKIM, and DMARC records, so each vendor's reputation and configuration are isolated.
Does using a subdomain hurt brand recognition?
The visible From can still show your brand name; recipients rarely notice the subdomain, and providers reward the isolation.
Why does subdomain delegation for email vendors matter for deliverability?
One SPF record cannot hold every vendor without exceeding the lookup limit, and one shared domain means one vendor's mistakes damage everyone's placement.
What is the first step to get started with subdomain delegation for email vendors?
List every vendor that sends as your brand.
What is the most common subdomain delegation for email vendors mistake?
Delegating the whole zone to a vendor via NS records, giving them control over more than mail.