# Error: 550 Requested action not taken: address does not exist or was rejected

Source: https://catalystgroup.gg/docs/email-delivery/error-550-recipient-rejected/
Updated: 2026-10-19 · By Duane Garner

The server permanently refused the message for this recipient: the mailbox does not exist, relaying was denied, or a policy blocked it.

> **Shown by SMTP-based sending (Other SMTP, Zoho Mail, the backup SMTP transport):** The test result or the error log shows a reply starting with `550`, for example `550 5.1.1 User unknown`, `550 5.7.1 Relaying denied` or `550 Requested action not taken: mailbox unavailable`.

 

This article is for site owners sending through an SMTP server who get a 550 reply. CRM-NG SMTP links here for any 550 that is not a "host unknown" reply.

 

## What this error means

 

Reply code 550 is a permanent refusal. The server will not take this message, and sending it again unchanged will fail the same way. The detail code after 550 tells you why:

 
- **5.1.1** and similar: the recipient's mailbox does not exist.
- **5.7.1** "relaying denied": the server will not pass mail on for you, usually because you are not logged in.
- **5.7.x** with words like "spam", "policy", "SPF" or "DMARC": the message or sender failed a check.

 

## Common causes

 
- A typo in the recipient address, or a mailbox that has been closed.
- **Authentication** is off in CRM-NG SMTP, so the server treats you as a stranger and refuses to relay to outside domains.
- The **From Email** domain fails SPF or DMARC, so the recipient's server rejects it.
- Your server's IP or your provider's IP is on a blocklist used by the recipient.
- The recipient's server considers the content to be spam.
- The recipient's mailbox is full and the server reports that permanently.

 

## How to fix

 
1. Read the full reply
  Open the error in **CRM-NG SMTP → Tools → Debug Events** and note the detail code and wording.
2. For unknown users: fix the address
  Check the spelling and confirm with the recipient. Update it in the plugin, form or user profile that sent the email.
3. For relaying denied: log in
  Go to **CRM-NG SMTP → Settings → General**. Turn on **Authentication** and enter **SMTP Username** and **SMTP Password**. Save.
4. For policy rejections: fix authentication
  Publish SPF, DKIM and DMARC for the domain in **From Email**, as your mail provider describes. Turn on **Force From Email** so every message uses that domain.
5. For blocklists
  Check your sending IP on a public blocklist checker. Ask your mail provider or host to help with delisting.
6. Send a test
  Go to **CRM-NG SMTP → Tools → Email Test**, fill in **Send To** and press **Send Email**.

 

## Verify it worked

 

The test page shows "Test email sent successfully! Check your inbox to confirm delivery." Check the **Deliverability and domain authentication** results on the same page for SPF and DMARC.

 

## Notes

 
- Repeated sends to addresses that do not exist hurt your sending reputation. Remove dead addresses from lists and user records.
- The [backup SMTP transport](https://catalystgroup.gg/docs/email-delivery/backup-smtp-transport/) never retries permanent recipient errors.

 

## Related

 
- [Other SMTP mailer guide](https://catalystgroup.gg/docs/email-delivery/mailer-other-smtp/)
- [Zoho Mail mailer guide](https://catalystgroup.gg/docs/email-delivery/mailer-zoho/)
- [DNS records for email](https://catalystgroup.gg/docs/email-delivery/dns-records/)
- [Emails landing in spam](https://catalystgroup.gg/docs/email-delivery/emails-landing-in-spam/)
- [Force From Email](https://catalystgroup.gg/docs/email-delivery/force-from-email/)
- [Error: Email address in suppression list](https://catalystgroup.gg/docs/email-delivery/error-email-in-suppression-list/)
- [Troubleshooting email delivery](https://catalystgroup.gg/docs/email-delivery/troubleshooting/)