By default, inboxes use @openmail.sh addresses. With a custom domain you can use any domain you own — for example agent@yourdomain.com.
How it works
- Add your domain in the dashboard
- OpenMail returns the DNS records you need to set
- Once DNS propagates, verify the domain
- Create inboxes on it by passing the domain when you create an inbox
Adding a domain
Go to Settings → Domains in the dashboard and click Add domain. Enter the domain you want to use (e.g. mail.acme.com).
You can use a subdomain like mail.acme.com or an apex domain like acme.com. A subdomain is generally easier to configure without affecting other email on your domain.
DNS records
| Type | Host | Value |
|---|
| MX | @ (or your subdomain) | mxa.mailgun.org (priority 10) |
| MX | @ (or your subdomain) | mxb.mailgun.org (priority 10) |
| TXT | @ (or your subdomain) | v=spf1 include:spf.openmail.sh ~all |
| TXT | openmail._domainkey (+ your subdomain) | Provided by OpenMail |
include:spf.openmail.sh to the existing record rather than creating a new one.
DKIM record adds a cryptographic signature to outbound email, proving messages were sent by you. The value is unique to your account and provided after you add the domain.
DNS changes typically propagate within minutes but can take up to 48 hours.
Verifying your domain
Once you’ve set your DNS records, click Verify in the dashboard. OpenMail checks all three record types and updates the domain status to verified.
If verification fails, double-check each record at your registrar and try again. Common issues:
- Existing MX records that weren’t replaced
- SPF record merged incorrectly (only one
v=spf1 per domain is allowed)
- DKIM host copied without the subdomain suffix
Using your domain
Once a domain shows as Verified, it is ready to use — there is no separate activation step. Verifying the domain is what makes it available.
Your account default domain never switches automatically. To create an inbox on your custom domain, choose it explicitly:
curl -X POST https://api.openmail.sh/v1/inboxes \
-H "Authorization: Bearer $OPENMAIL_API_KEY" \
-H "Content-Type: application/json" \
-d '{
"mailboxName": "support",
"domain": "yourdomain.com"
}'
{mailboxName}@yourdomain.com
domain, the inbox is created on your account default domain (for example @openmail.sh). Passing a domain that is not verified or does not belong to your account returns invalid_domain.
Limits
Custom domains are available on the Developer plan and above.
| Plan | Custom domains |
|---|
| Free | — |
| Developer | 10 |
| Launch | 150 |
| Enterprise | Custom |
Removing a domain
You can delete a custom domain from the dashboard as long as it has no inboxes. Delete the inboxes on that domain first, then remove the domain.
Deleting a domain removes it from OpenMail but does not delete your DNS records — you can remove those from your registrar separately. 
