Sending domain
The domain your mail is sent and authenticated from, mainly the visible From domain and the DKIM signing domain, on which providers build domain reputation.
What it means
Several domains appear in a message: the Return-Path (envelope sender), the visible From, the DKIM signing domain, the HELO name and the link domains. Providers judge all of them, and DMARC requires the From domain to align with the SPF or DKIM domain. When people say sending domain they usually mean the From domain and the authenticated domain behind it.
M3AAWG recommends that senders using an ESP authenticate with their own domain or subdomain rather than the ESP's, so they build their own reputation, and use subdomains named for each purpose (offers.example.com for marketing, info.example.com for transactional). Google counts all subdomains of a primary domain together toward its 5,000-a-day bulk sender threshold.
A new sending domain or subdomain needs warming up.
Related terms
On this site
Sources
What this definition rests on. The wording is ours; the facts are theirs.
- M3AAWG Sender Best Common Practices, version 4.0 (August 2026)m3aawg.org
- Google: Email sender guidelines FAQsupport.google.com
- Google: Email sender guidelinessupport.google.com
All 432 terms in the glossaryThe wiki: blocklists and bounce codes