A sending domain is the domain your marketing emails are sent from and checked against by email authentication, such as the “yourbrand.co.uk” in hello@yourbrand.co.uk, or a subdomain like news.yourbrand.co.uk set aside for marketing. Mailbox providers use it to decide who is responsible for a message and whose reputation it affects.
How a sending domain works
A single email can carry more than one domain, which is where most of the confusion starts:
- The from domain is the one readers see in the from address.
- The envelope domain Also called the return-path or bounce domain, is used behind the scenes to collect bounces. Email platforms often set this to their own domain unless you configure a custom one.
- The DKIM signing domain is the domain that digitally signs the message to prove it has not been altered.
For DMARC to pass, the domain in the from address must align with a domain that passes SPF or DKIM. In practice, that means adding the DNS records your email platform gives you, so it can sign mail as your domain rather than its own. Until you do, many platforms send on your behalf under a shared domain, and Gmail may show a “via” note beside your name.
Subdomain sending means using a dedicated subdomain for marketing while staff email stays on the main domain. Providers can track reputation for each subdomain, although persistent bad behaviour on a subdomain can still reflect on its parent.
Why it matters
Your sending domain carries your reputation. Set up properly, the trust you build stays with you if you change platform. Left on defaults, you are relying on a shared reputation and can be judged alongside other senders’ habits.
Authentication is no longer optional for anyone sending in volume. Gmail and Yahoo require high-volume senders to authenticate their own domain and publish a DMARC record, and Microsoft introduced similar requirements for Outlook.com addresses in 2025. A UK business emailing customers at those providers without a properly configured sending domain risks having its mail rejected.
Keeping marketing on a subdomain also protects day-to-day email. If a campaign draws complaints, the subdomain takes the first hit, not the domain your accounts team uses to send invoices.
Common mistakes
- Leaving the platform’s default domain in place. It works on day one, but you never build a reputation of your own and alignment may fail.
- Sending from a lookalike domain. Using yourbrand-mail.com instead of a subdomain of yourbrand.co.uk looks like phishing, both to filters and to customers.
- Launching a new subdomain at full volume. A new subdomain has no history. Build up gradually, as covered in domain warming.
- Too many SPF lookups. Every service that sends for you, from the CRM to the help desk to the invoicing tool, adds to your SPF record, and SPF fails once it needs more than ten DNS lookups.
- Ignoring the link domain. If every link in your email runs through a tracking domain shared with thousands of other senders, set up a branded tracking domain where your platform allows it.
How to act on it
Decide on one domain or subdomain for marketing and stick with it. In your email platform’s domain settings, add the DKIM and return-path records it provides to your DNS, make sure SPF includes the platform, and publish a DMARC record, starting with a monitoring policy so you can see who sends as your domain before you tighten it. Then send a test to a Gmail address and use “Show original” to confirm that SPF, DKIM and DMARC all show PASS.
Keep a short list of every service allowed to send as your domain, with a named owner for each. It saves a lot of guesswork when something breaks or someone leaves.
If this sits on your to-do list next to bigger questions about which channels deserve investment, a digital marketing strategy engagement is where I would start.