What is a sending subdomain?

A sending subdomain is a domain prefix that creates separation within your primary domain. Instead of sending from company.com, you might send from outreach.company.com or mail.company.com.

How subdomains work: Each subdomain can have its own SPF, DKIM, and DMARC configuration. Mailbox providers track reputation at the subdomain level to varying degrees, providing some isolation from your root domain.

Subdomain vs separate domain: Subdomains maintain brand connection and are easier to set up than entirely new domains. However, reputation problems can still affect the parent domain, especially for severe issues like Spamhaus listings.

Common patterns:

mail.company.com for transactional

news.company.com for newsletters

outreach.company.com for cold campaigns

Subdomains provide organization and some isolation, but they're not a complete firewall. For cold outreach with significant risk, separate root domains offer stronger protection.