# 553 5.1.2 Bounce: Recipient Domain Not Found URL: https://email-validation.org/bounce-codes/553-5-1-2/ Updated: 2026-11-06 > Documentation index: https://email-validation.org/llms.txt **At a glance** - **Type:** permanent failure (class 5, RFC 3463 §2). The sending server does not retry; sending the same message again fails the same way until the cause is fixed. - **Basic code 553:** “Requested action not taken: mailbox name not allowed (e.g., mailbox syntax incorrect)” (RFC 5321 §4.2.3). - **Enhanced code 5.1.2:** “Bad destination system address” in the IANA registry (RFC 3463), in the group addressing status (RFC 3463 §3.2). The part after the @ is the problem: the domain does not exist, or it cannot receive mail. No retry will help until the domain itself is fixed, so the address is undeliverable as written. ## What it means [RFC 3463 §3.2](https://www.rfc-editor.org/rfc/rfc3463) defines X.1.2 as a bad destination system address. For an Internet address, that means the portion to the right of the @ is not valid for mail. Like 5.1.1, it is only meant for permanent failures. The basic code 553 says the mailbox name is not allowed ([RFC 5321 §4.2.3](https://www.rfc-editor.org/rfc/rfc5321)). Before a server sends, it looks up the recipient domain in DNS. [RFC 5321 §5.1](https://www.rfc-editor.org/rfc/rfc5321) says that if the lookup returns "domain does not exist", this must be reported as an error. A temporary DNS failure is handled differently: the message must be queued and retried later. ## Common causes - A misspelled domain: `gmial.com`, `outlok.com`, `yahoo.con`. - A wrong or missing top-level domain, such as `example.co` for `example.com`. - A company domain that expired, was sold, or was retired after a merger or rebrand. - A domain that exists for a website but was never set up to receive email. ## How providers use it **Gmail** returns 553 5.1.2 when it cannot find the recipient domain, and asks you to check the address for typos ([Google's SMTP error reference](https://support.google.com/a/answer/3726730)). Other systems may report the same situation with a plain 550, or with [5.4.4 unable to route](https://email-validation.org/bounce-codes/5-4-4/) when the domain exists in DNS but no mail server can be found for it. A domain that has deliberately published "no mail here" in DNS is reported as [556 5.1.10](https://email-validation.org/bounce-codes/556-5-1-10/). ## How to fix it 1. Read the domain in the bounce closely. A swapped or missing letter is easy to miss at a glance. 2. Look up the domain's MX records, for example with `dig MX example.com`. An NXDOMAIN answer means the domain does not exist. 3. If you own the domain, check that it is still registered and that its MX records point to your mail service. 4. If the contact's organization changed its domain, ask them for their current address. ## What to do with the address Treat it as a hard bounce and suppress it. If the typo is obvious and you can confirm the right spelling with the person, update the record; otherwise remove it. Do not "fix" a domain by guessing, since a guessed address may belong to someone else. To catch bad domains when people type them, check addresses on your forms with the [email checker](https://email-validation.org/email-checker/). ## Related codes - [550 5.1.1](https://email-validation.org/bounce-codes/550-5-1-1/): The recipient mailbox does not exist - [556 5.1.10](https://email-validation.org/bounce-codes/556-5-1-10/): The recipient domain publishes a null MX: it takes no mail - [5.4.4](https://email-validation.org/bounce-codes/5-4-4/): Unable to route: no mail server found for the domain - [553 5.1.3](https://email-validation.org/bounce-codes/553-5-1-3/): The recipient address is not valid syntax See [every bounce code](https://email-validation.org/bounce-codes/) in the dictionary. Many bounces from addresses that do not exist can be avoided: check an address with our [free email checker](https://email-validation.org/email-checker/), or [clean a whole list](https://email-validation.org/bulk-email-verification/) before you send.