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Use a custom domain when you want branded mailbox addresses such as support@example.com. A domain must be verified before you can create mailboxes on it.

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Shared vs custom domains

OptionBest forDNS required
myagent.mx shared domainFast tests and simple agentsNo
Custom domainProduction mail and branded addressesYes
Each team starts with 25 domains. See Team limits.

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Add a domain

1

Open Domains

Open Domains in the team workspace and select Add domain.
2

Enter the domain

Enter the domain you own, such as mail.example.com or example.com.
3

Copy DNS records

Sendmux shows the records needed for ownership, inbound routing, sending policy, message policy, and email signing.
4

Publish the records

Add each record at your DNS provider. Copy values exactly as shown.
5

Verify

Select Verify after the records have propagated. The domain is ready when all records show as ready.

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DNS records

PurposeRecordWhat it does
OwnershipTXTConfirms you control the domain.
Receive mailMXRoutes inbound mail for the domain to Sendmux.
Email signingCNAMEEnables DKIM signing through Amazon SES.
Sending policyTXTAuthorises Sendmux to send for the domain.
Message policyTXTDefines DMARC handling for suspicious mail.
You can download the records as a zone file from the domain detail page.

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Verification states

StateMeaning
pendingRecords are missing, still propagating, or still being checked.
verifiedAll required records are present and ready.
failedOne or more records could not be verified after repeated checks.
Sendmux rechecks domains every six hours. A short DNS issue does not immediately trigger an email. Persistent failures notify team owners.

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Troubleshooting

Check that the TXT record name and value match Sendmux exactly. Some DNS providers append the zone name automatically, which can duplicate the domain.
Check that the MX record is on the same domain you added to Sendmux. DNS proxying features do not apply to MX records.
Keep only one SPF record for the same domain name. Merge all include: values into the same TXT record.
Check that the TXT record is published at _dmarc.{your - domain} and still includes the policy value Sendmux generated.
DKIM records can take longer to verify. Confirm all three CNAME records are present, then wait and verify again.

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Delete a domain

Deletion is blocked while active mailboxes still use the domain. Delete or move those mailboxes first, then delete the domain. After deletion, remove the DNS records from your DNS provider if you no longer need them.

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API access

Use the Management API when you want to create, list, verify, or delete domains from your own tooling. Keep API shape, permissions, and error handling in the generated reference so your client follows the current contract.

Management API

Open the generated Domains endpoint reference.

Mailboxes

Create addresses on verified domains.

Domain settings

See the coming-soon inbound handling controls.

Sending accounts

Connect providers for outbound sending.

Team limits

Request more domain capacity.