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Cisco Secure Email (formerly IronPort) · temporary error

451 4.7.1: DMARC could not be checked

A temporary failure stopped the Cisco gateway from verifying DMARC for your message, and its policy defers such mail, so your server should retry.

Cisco Secure Email
Provider
Temporary (4xx)
Class
Sources checked
By , email deliverability consultant
Author

At a glance

Code
451 4.7.1
Temporary or permanent
TemporaryThe sending server keeps the message and tries again later.
Who has to act
The sender. The fix is on the sending side: your domain, your server or your list.
What the server says
451 4.7.1 #4.7.1 Unable to perform DMARC verification

What it means

Cisco’s DMARC profiles let an administrator either accept or reject messages whose DMARC check fails temporarily. When they choose to reject, the gateway sends this default temporary reply. A temporary failure means the check could not be completed this time, usually because a DNS lookup for the DMARC, SPF or DKIM records timed out. Your server keeps the message and retries, and a later attempt normally succeeds. Repeated deferrals point to DNS for your domain that answers slowly or unreliably.

Common causes

  • DNS servers for your domain did not answer in time.
  • A lookup for your DKIM key or SPF includes failed temporarily.
  • A short DNS problem on the receiving side.

How to fix it

  1. 01Let your server retry the message.
  2. 02Check that your DMARC, SPF and DKIM records resolve quickly from more than one network.
  3. 03Move to more reliable DNS hosting if lookups often time out.

Sources

What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.

  1. 451Local error in processing.The receiving server hit a problem on its own side while handling the message and stopped. The reply is temporary, so the sending server will try again.StandardTemporary
  2. 550 5.7.1Rejected under your domain’s DMARC policy.Your message failed DMARC, your domain’s DMARC record asks receivers to reject such mail, and the recipient’s Cisco gateway did so.Cisco Secure EmailPermanent

Further reading

All 7 Cisco Secure Email codesEvery code in the wikiPaste your own bounce

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example.comWatching
  • SPFpass
  • DKIMpass
  • DMARCp=none
  • Blacklists0 of 33

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