Give Your AI Agent an Address on Your Own Domain
A hosted address is fine for testing. When your agent talks to customers and vendors, move it to a subdomain you own with this checklist.
By Toan Nhu
Picture your agent emailing a real vendor for the first time. The message is clear and useful, but it comes from a random hosted address the vendor has never seen. The likely reply is a polite "Is this a bot?" or no reply at all. Nothing was wrong with the content. The address made it look like a test account.
Your agent's address is part of its identity
People decide whether to trust an email before they read it. They look at the sender, then the domain, then the subject. An agent writing from a domain they recognize reads like part of your company. An agent writing from a shared domain reads like an experiment, even when it is doing real work.
That matters most when the agent:
- Writes to customers, vendors, or partners who know your brand.
- Receives replies that should land in an inbox your team controls.
- Signs up for services that later send invoices, receipts, or security notices.
- Needs to keep the same address after you go to production.
Why "we will switch later" costs more than it looks
Starting on a hosted address is the right call for prototypes. The trouble starts when the hosted address leaks into real use:
- Contacts save the old address. Replies, forwarded threads, and vendor records keep pointing at it.
- Accounts are registered to it. Every service your agent signed up for now has the wrong contact email.
- DNS gets rushed. Teams copy SPF, DKIM, and MX records in a hurry on launch day, guess a value, and break mail for the main domain.
- Reputation starts from zero. A new sending domain has no history, and blasting it on day one is how agent mail lands in spam.
The fix is not complicated. Decide early which address the agent will ship with, and set it up calmly before real traffic depends on it.
Hosted or custom: a quick decision
Stay on a hosted Mermail address when the agent is internal, short-lived, or still in testing. Every plan includes hosted mailboxes, and SPF, DKIM, and DMARC are managed for you on the Mermail domain.
Move to your own domain when the agent talks to people outside your team, when replies matter, or when the address will outlive the prototype. On Mermail, custom domains are a paid feature: the Developer plan includes one custom domain per workspace.
How Mermail handles your domain
Mermail's custom domains guide is built around three steps in the console: choose the domain, add the DNS records Mermail generates, and verify. A few details are worth knowing before you start:
- One domain per workspace. When it is fully connected, every mailbox in the workspace moves to it and keeps its username. support@mermail.app becomes support@mail.example.com.
- Existing mail stays. Moving to the domain does not delete stored messages.
- Domains with existing email are rejected. If the domain already has MX records, Mermail suggests a subdomain instead, so your company mail stays untouched.
- Sending and receiving verify separately. The domain is ready when both Sending ready and Receiving ready appear.
- DMARC is yours to add. Mermail signs mail with SPF and DKIM once the records verify, and recommends you publish a DMARC record yourself.
- The API can do it too. Developer workspaces can add, verify, list, and delete email domains through the Mermail API.
Setup checklist
1. Pick a dedicated subdomain
Use something like mail.example.com or agents.example.com. It keeps agent traffic away from your main domain's MX records and gives the agent its own sending reputation. If you plan to run many agents, read custom domains for agent inboxes first.
2. Review every mailbox in the workspace
Because the whole workspace moves to the domain, check each mailbox username before you connect. If an address already exists on the domain, Mermail shows a conflict and waits for you to resolve it.
3. Add the domain in the console
Open Custom Domains in the Mermail console, enter the subdomain, and click Check domain. You need workspace admin access and permission to edit DNS for the domain.
4. Publish the records exactly as shown
Copy each record from Mermail into your DNS provider. Two mistakes cause most failures:
- Proxied CNAMEs. Set every CNAME to DNS only. A proxied record returns IP addresses instead of the target and never verifies.
- Doubled names. Some providers append the zone automatically. If a record ends up at name.example.com.example.com, enter only the part before your zone.
Do not add guessed SPF, DKIM, or MX values, and keep existing records the list does not replace.
5. Verify, then add DMARC
Click Check connection. Mermail explains what it found for each record that is not verified yet, so you can fix it and check again. Once both capabilities are ready, add a TXT record at _dmarc on your subdomain. Start relaxed and tighten later:
_dmarc.mail.example.com TXT "v=DMARC1; p=none; rua=mailto:dmarc@mail.example.com"Our SPF, DKIM, and DMARC guide explains when to move to quarantine and reject.
6. Test both directions
Send one message to an external inbox you control, check the sender and signature, and reply. Confirm the reply shows up in Mermail. One successful test does not prove delivery everywhere, so watch bounces and complaints as volume grows. See monitoring your sending domain.
7. Ramp up slowly
Start with a small number of messages to people who expect them. Increase volume only while delivery stays healthy. Keep outbound replies as human-approved drafts at first, so a person sees what the agent sends from your brand.
What happens if you change plans or domains
- If the workspace moves to the Free plan, the domain is paused and mailboxes return to a Mermail-hosted address until you upgrade again.
- If you remove the domain, every mailbox switches back to its @mermail.app address and stored mail stays intact. To use the domain again, you add and verify it from scratch.
- To use a different domain, remove the current one first.
FAQ
Can I use a custom domain on the Mermail Free plan?
No. Custom domains require a paid plan. The Developer plan includes one custom domain per workspace. Free workspaces use a Mermail-hosted address.
Can I connect my main company domain?
Not if it already receives email. Mermail rejects domains that already have MX records and suggests a subdomain such as mail.example.com, which keeps your existing mail safe.
Will my agent's existing mail disappear when I connect a domain?
No. Mailboxes move to the new domain and keep their usernames. Existing mail stays in place.
Does Mermail set up DMARC for me?
Mermail signs mail with SPF and DKIM after verification. You add the DMARC record yourself at _dmarc on your domain.
Can my agent set up the domain through the API?
Developer workspaces can add, verify, list, and delete email domains through the Mermail API. A person with DNS access still has to publish the records.
