# Error: 451 Temporary local problem or timeout

Source: https://catalystgroup.gg/docs/email-delivery/error-451-temporary-server-problem/
Updated: 2026-10-19 · By Duane Garner

The mail server hit a temporary problem of its own while handling your message. Retry later; if it persists, check DNS and reputation.

> **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 `451`, for example `451 Requested action aborted: local error in processing` or `451 4.7.1 Please try again later`.

 

This article is for site owners sending through an SMTP server who get a 451 reply.

 

## What this error means

 

Reply code 451 means the server started handling your message and then had to stop because of a problem on its side. The 4 at the start means temporary. The server is asking you to try again later; it has not judged your message or settings to be wrong.

 

The detail after the code helps narrow it down. 4.7.x usually means a policy or spam check could not finish; 4.3.0 or 4.4.x point to the server or network; 4.1.8 or similar point to a DNS lookup on your sender domain.

 

## Common causes

 
- The server is busy, low on resources or restarting.
- A spam or virus scanner on the server timed out while checking your message.
- Greylisting: the first attempt from an unfamiliar sender is refused on purpose.
- The server could not look up DNS for your sender domain, or your domain's DNS answered slowly.
- Your server's IP is on a temporary watch list because of recent volume or complaints.
- A problem further along, where your provider relays the message to the recipient's server.

 

## How to fix

 
1. Retry after a few minutes
  Go to **CRM-NG SMTP → Tools → Email Test**, fill in **Send To** and press **Send Email**.
2. Read the full reply
  Open the error in **CRM-NG SMTP → Tools → Debug Events** and note the detail code and any words such as "DNS", "policy" or "greylisted".
3. Check your domain's DNS
  If the reply mentions your sender domain, confirm the domain in **From Email** on **CRM-NG SMTP → Settings → General** has working MX and SPF records. A public DNS lookup tool shows them.
4. Spread out sending
  If 451 appears during bursts, set **Email Rate Limiting** on **CRM-NG SMTP → Settings → Misc**.
5. Contact your mail provider
  If 451 continues for more than an hour, send the provider the full reply and the time of the attempt.

 

## Verify it worked

 

The test page shows "Test email sent successfully! Check your inbox to confirm delivery." Later messages go through without new 451 entries in the Email Log.

 

## Notes

 
- A [backup SMTP transport](https://catalystgroup.gg/docs/email-delivery/backup-smtp-transport/) on the **Alerts** tab can carry mail while the main server has temporary problems.
- Messages refused with 451 are not queued for retry by CRM-NG SMTP. If you store bodies in the Email Log, use **Resend email** on the failed entry once the server recovers.

 

## 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/)
- [Error: 421 Connection timeout: network issues](https://catalystgroup.gg/docs/email-delivery/error-421-connection-timeout/)
- [Error: 450 Requested mail action not taken: mailbox unavailable](https://catalystgroup.gg/docs/email-delivery/error-450-mailbox-unavailable/)
- [Troubleshooting email delivery](https://catalystgroup.gg/docs/email-delivery/troubleshooting/)