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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

If you’re using a Free team, you can have 1 domain. Check your current limit on the Domains page. Free limits are fixed. If you need more capacity, delete an unused domain or upgrade to Pro. 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. For DMARC, verification checks only that a TXT record at _dmarc.{your-domain} contains v=DMARC1. You can keep your existing policy.

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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 DNS every six hours. A short DNS issue does not immediately trigger an email. Persistent failures notify team owners. Amazon SES status is checked separately on a five-minute schedule, even when DNS checks cannot complete. This schedule does not guarantee an update within five minutes. Your domain list and detail page refresh while visible and when you return to the tab. The Action required label includes a temporary Amazon SES authentication failure. Review the individual status checks and the last-checked time. For previously verified managed domains, Sendmux compares authentication status reported by Amazon SES, including DKIM. It creates an alert when authentication degrades, worsens or fully recovers. Repeated observations of the same status do not create duplicate alerts. Team owners choose email and in-app notices, including recovery notices, in their Deliverability notification preferences. Alerts that include disabled sending or signing use both channels for active owners and admins, even if those channels are disabled in their preferences. Email notices can arrive after the status update. Managed sending from your custom domain requires a successful Amazon SES identity check, sending enabled, healthy DKIM and signing enabled. If custom MAIL FROM is configured, it must also be healthy and match the configured domain. Checks expire after one hour. Missing, incomplete, unhealthy or older checks block managed sending, including saved mailbox drafts, and remove its options from mailbox sender choices until verification and a fresh, healthy check succeed. Connected sending accounts keep their existing rules.

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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.
Publish a TXT record containing v=DMARC1 at _dmarc.{your-domain}. The policy and other fields do not affect verification.
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.