Email Subdomain Setup for Receive-Only Inboxes

For an email subdomain such as inbox.example.com, publish its own MX record pointing to your mail-server hostname, then configure the receiver to accept addresses ending in @inbox.example.com. This isolates temporary or QA mail from the root domain’s workplace MX records.

DNS and mailbox acceptance are separate jobs

DNS delegation can be granular. The root may continue receiving employee mail through one provider while a subdomain routes test or temporary mail to a separate VPS. This reduces the blast radius of changes and keeps responsibilities clear.

The local part and domain together form the mailbox identity. user@inbox.example.com is not the same address as user@example.com, so application login, server routing, and support documentation must preserve the full string.

Plan the mail route before changing records

Choose a descriptive subdomain that does not imply outbound business correspondence. Add a stable mail-host record, publish the MX on the subdomain, install TLS for the mail host, and add only that subdomain to the receiver.

Document rollback before changing DNS. If the new service fails, removing or replacing the subdomain MX should not disturb the root mail provider.

Configure the receiving path in order

1. Inventory current root MX records and leave them unchanged.
Complete this part before you create the receiving mail-host address record. For email subdomain setup, changing several variables together makes the result harder to interpret and repeat.
2. Create the receiving mail-host address record.
Complete this part before you add an mx record specifically on the subdomain label. For email subdomain setup, changing several variables together makes the result harder to interpret and repeat.
3. Add an MX record specifically on the subdomain label.
Complete this part before you configure smtp, filtering, application acceptance and tls. For email subdomain setup, changing several variables together makes the result harder to interpret and repeat.
4. Configure SMTP, filtering, application acceptance and TLS.
Complete this part before you test externally, monitor logs, then expose the domain to users. For email subdomain setup, changing several variables together makes the result harder to interpret and repeat.
5. Test externally, monitor logs, then expose the domain to users.
Complete this part before you inventory current root mx records and leave them unchanged. For email subdomain setup, changing several variables together makes the result harder to interpret and repeat.

Prove the route with an outside sender

Query both the root and subdomain MX results to confirm they intentionally differ. Test an address at each and verify mail reaches the correct provider.

Check documentation and UI truncation so users can see the entire subdomain address. A hidden suffix can cause wrong-recipient mistakes.

DNS mistakes that look correct in a control panel

Avoid: Replacing root MX records instead of adding subdomain MX

A better response is to inventory current root mx records and leave them unchanged, then query both the root and subdomain mx results to confirm they intentionally differ. That keeps the email subdomain setup decision tied to an observable result instead of an assumption.

Avoid: Adding only an A record and expecting mail routing

A better response is to create the receiving mail-host address record, then check documentation and ui truncation so users can see the entire subdomain address. That keeps the email subdomain setup decision tied to an observable result instead of an assumption.

Avoid: Forgetting the subdomain in Postfix or application configuration

A better response is to add an mx record specifically on the subdomain label, then query both the root and subdomain mx results to confirm they intentionally differ. That keeps the email subdomain setup decision tied to an observable result instead of an assumption.

Avoid: Advertising the domain before an external delivery test

A better response is to configure smtp, filtering, application acceptance and tls, then check documentation and ui truncation so users can see the entire subdomain address. That keeps the email subdomain setup decision tied to an observable result instead of an assumption.

Operational limits of receive-only domains

A separate subdomain limits routing impact but still exposes a public SMTP service. Apply spam, rate, size, monitoring, abuse and retention controls.

If the same organizational domain is used for sending elsewhere, publish authentication records for that specific sending path; inbound MX alone does not create outbound trust.

How TempMail Cloud handles approved domains

TempMail Cloud can list multiple active receiving subdomains. Once DNS routes correctly, the administrator adds the exact domain and automated receiver synchronization makes it available for mailbox generation.

The platform’s main website remains on tempmail.cloud; adding a receiving subdomain does not automatically host the web interface there.

Frequently Asked Questions

Continue with the custom-domain receiving guides

• For the broader workflow, read Create an address on a custom domain when working through email subdomain setup.
• For a closely related decision, see Receive-only business email explained when working through email subdomain setup.
• Keep this companion guide nearby: Temporary email with saved login when working through email subdomain setup.

For email subdomain setup, remember that TempMail Cloud is receive-only. Check the safety guidance before using an address for an important account, and see the editorial standards for how this guide is maintained.

Primary references used for this guide

• Cloudflare guidance for email DNS records — consulted for the email subdomain setup recommendations above.
• IETF Simple Mail Transfer Protocol — consulted for the email subdomain setup recommendations above.