Domain reputation is the part of sender reputation attached to the domain in your From address and DKIM signature. Because it follows the domain wherever you send from, it matters more today than the reputation of any one server.
Why it matters more than IP reputation
With Google Workspace or Microsoft 365 mailboxes, you share the provider's sending IPs with many other customers. The provider's IPs are well kept, so what separates your email from everyone else's is your domain's own history.
How to protect it
- Send cold email from separate domains, never your main one, so a bad campaign can't hurt your invoices and customer replies.
- Give new domains time: a domain a few weeks old, warmed up, does far better than one bought yesterday.
- Keep bounces under 2% and complaints under 0.1%.
- Spread volume across several domains and mailboxes.
Checking it
Providers don't publish a domain score; Google stopped showing one in Postmaster Tools in 2025. mailzy rates each domain from evidence it can measure: warm-up and test inbox placement, authentication, bounces and blocklists.