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Use a custom domain when you want branded sending, hosted mailboxes, or both. Choose the domain mode when you add it: sending only avoids MX changes, while sending & receiving lets you create mailboxes after verification.

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Domain options

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

Choose usage

Choose Sending only if Sendmux should only send from the domain. Choose Sending & receiving if Sendmux should also receive mail and host mailboxes on the domain.
4

Copy DNS records

Sendmux shows the records required for your chosen usage. Sending-only domains do not show or check an MX record.
5

Publish the records

Add each record at your DNS provider. Copy values exactly as shown.
6

Verify

Select Verify after the records have propagated. Sending-only domains check ownership, sending policy, message policy, email signing, and bounce handling. Sending & receiving domains also check inbound routing.

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DNS records

You can download the records as a zone file from the domain detail page.

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Enable receiving later

Open the sending-only domain and choose Switch to sending & receiving. Sendmux adds the MX requirement, resets the domain to pending, and asks you to verify again. Add the MX record before creating mailboxes.

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Verification states

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.
This only applies to sending & receiving domains. 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 the MX and TXT records on the bounce.{your-domain} subdomain. The MX record must use the target Sendmux shows, and the TXT record must match the generated SPF value.
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

Deleting a sending-only domain stops sending from it. Deleting a sending & receiving domain is blocked while active mailboxes still use it. 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, upgrade, 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 sending & receiving domains.

Domain settings

Review inbound controls for sending & receiving domains.

Sending accounts

Connect providers for outbound sending.

Team limits

Request more domain capacity.