# Troubleshooting SMTP 530 Errors (Gmail, Yahoo, and Custom Domains)

Diagnose SMTP 530 errors by validating MX records, authentication settings, and domain routing configuration for MailSlurp custom domains.

A `530` SMTP error usually means the sender is not authorized for the action it attempted.

In MailSlurp custom-domain setups, the most common cause is DNS misconfiguration (especially incorrect MX records).

## What `530` typically means

Depending on provider, `530` often maps to one of these conditions:

- authentication required but missing
- sender not permitted for this route
- domain routing records are incorrect
- SMTP host intended for internal/private use is being used publicly

## Fast triage checklist

1. Verify your domain MX records.
2. Confirm you are using the public inbound MX endpoint.
3. Check SPF/DKIM/DMARC health for sender identity.
4. Confirm app credentials and sender envelope are valid.

## Critical MX record rule for custom domains

For inbound handling, use only the public inbound endpoint record for your region.

Example expected value (us-west-2):

```text
10 inbound-smtp.us-west-2.amazonaws.com.
```

If you accidentally publish a private/internal SMTP hostname, Gmail/Yahoo and other providers may reject with `530` or related authorization errors.

## Validate MX records with dig

```bash
dig your-domain.com mx
```

Expected pattern:

```text
your-domain.com.  600 IN MX 10 inbound-smtp.us-west-2.amazonaws.com.
```

Notes:

- the trailing dot is valid DNS notation
- avoid duplicate or conflicting MX records during migration
- allow DNS propagation time before retesting

## Secondary checks when MX looks correct

- sender domain/auth alignment (SPF/DKIM/DMARC)
- wrong SMTP host/port for outbound path
- stale credentials in app config or secret store
- misrouted subdomain inbox configuration

Useful tools:

- [DNS lookup](/tools/dns-lookup/)
- [SPF checker](/tools/spf-checker/)
- [DKIM checker](/tools/dkim-checker/)
- [DMARC checker](/tools/dmarc-checker/)

## If you use subdomains

If your inboxes are configured on a subdomain, ensure that subdomain has the correct MX/auth records and is fully onboarded for your account.

If records look correct but failures continue, contact support with:

- full SMTP error message
- sending domain/subdomain
- sample timestamp and recipient
- current MX/SPF/DKIM/DMARC outputs

Support: [/support/contact/](/support/contact/)