How a Reply Domain Works
Your ESP sends the campaign. The customer hits reply. That reply goes to whatever address sits in the Reply-To header, and you control that field. A reply domain puts an address you own on the receiving end of it, delivered to Know Reply instead of to a mailbox nobody watches.
You delegate one subdomain, for example reply.yourbrand.com. Your root domain, your existing mail, and your current MX records are untouched. Know Reply never receives mail addressed to yourbrand.com.
The four records
Section titled “The four records”Add the domain in Know Reply first. The app generates the exact values, because three of the four are unique to your domain. For reply.yourbrand.com you get:
| Type | Host | Value | What it does |
|---|---|---|---|
| MX | reply.yourbrand.com |
mx.sendgrid.net, priority 10 |
Receives the replies |
| CNAME | emNNNN.reply.yourbrand.com |
uNNNNNN.wlNNN.sendgrid.net |
Return path, so SPF aligns on outbound |
| CNAME | s1._domainkey.reply.yourbrand.com |
s1.domainkey.uNNNNNN.wlNNN.sendgrid.net |
DKIM signing key |
| CNAME | s2._domainkey.reply.yourbrand.com |
s2.domainkey.uNNNNNN.wlNNN.sendgrid.net |
DKIM signing key |
The NNNN parts are placeholders. Copy the real values from the domain screen, do not type them from this page.
One MX and three CNAMEs coexist on the same subdomain because the return-path CNAME sits on a deeper label (emNNNN.reply.yourbrand.com), not on reply.yourbrand.com itself. Inbound and outbound do not collide.
DMARC is optional and worth adding
Section titled “DMARC is optional and worth adding”A TXT record at _dmarc.reply.yourbrand.com with the value v=DMARC1; p=none; rua=mailto:you@yourbrand.com gives you reporting on anything sending as the subdomain. Start at p=none. A stricter policy on a subdomain you might reuse later is a way to lose your own mail.
Full host or relative host
Section titled “Full host or relative host”Providers disagree about the host field. Some want the fully qualified name, some append your domain for you and want only the part in front of it.
| Provider style | What to enter for the DKIM record |
|---|---|
| Appends your domain (Cloudflare, GoDaddy, Namecheap, Hostinger, Squarespace) | s1._domainkey.reply |
| Wants the full name (Route 53, most enterprise DNS) | s1._domainkey.reply.yourbrand.com |
The tell: type the full name into the field and look at the preview. If it shows s1._domainkey.reply.yourbrand.com.yourbrand.com, the provider is appending and you want the short form. Cloudflare and Route 53 both show a preview before you save.
Propagation is usually a few minutes. Say an hour before you start troubleshooting. The domain screen re-checks every 30 seconds while it is pending, and you can press Check DNS to force a check.
Any address on the domain works
Section titled “Any address on the domain works”Once the domain verifies, every local part on it receives mail. You do not register addresses in advance. hello@reply.yourbrand.com, orders@reply.yourbrand.com, and bfcm-2026@reply.yourbrand.com all work the moment you paste them into an ESP, and the address appears in your account list after the first reply arrives.
Use a different local part for each sending platform. It costs nothing, and it means your reporting tells you which platform a conversation came from. Later you can point each one at a different agent.
| Where you send from | Suggested Reply-To |
|---|---|
| Klaviyo | klaviyo@reply.yourbrand.com |
| Mailchimp | mailchimp@reply.yourbrand.com |
| Omnisend | omnisend@reply.yourbrand.com |
| Shopify Email and notifications | shop@reply.yourbrand.com |
| Brevo | brevo@reply.yourbrand.com |
| ActiveCampaign | ac@reply.yourbrand.com |
| Drip | drip@reply.yourbrand.com |
| SendGrid Marketing Campaigns | sendgrid@reply.yourbrand.com |
| HubSpot | hubspot@reply.yourbrand.com |
If you would rather keep it to one address, hello@reply.yourbrand.com is the default the app suggests and it works everywhere.
Addresses Know Reply will not answer
Section titled “Addresses Know Reply will not answer”postmaster, abuse, mailer-daemon, noreply, no-reply, bounce, and anything starting with bounce- or bounces- are never auto-answered. Those are automated addresses, and replying to them creates mail loops. Do not use them as your Reply-To.
Verification emails land in Know Reply, not your mailbox
Section titled “Verification emails land in Know Reply, not your mailbox”Several platforms verify a sender or reply-to address by emailing it a confirmation link. Omnisend, Drip, and SendGrid all do this. Because the MX record points the whole subdomain at Know Reply, that confirmation email arrives in your Know Reply workspace rather than in your inbox. Open the message in the workspace email view and click the link from there.
If a platform will not send to a subdomain at all, use a verified address on your root domain as the sender and put the reply subdomain address in the Reply-To field only. That is the normal arrangement anyway.
Order of work
Section titled “Order of work”- Add the domain in Know Reply and pick the agent that answers by default.
- Add the four records at your DNS provider. Cloudflare, GoDaddy, Namecheap, Squarespace, Hostinger, Route 53.
- Wait for the domain to show Verified.
- Set the Reply-To in each platform you send from. Pick your platform.
- Send yourself a test campaign and reply to it.
A domain that verifies and then receives nothing almost always means step 4 never happened, or it happened in one platform and not the others.
For the connection methods that watch an existing mailbox instead, see Connecting Email.