451 4.4.3: SPF could not be checked
The Cisco gateway could not complete an SPF check for your domain because of a temporary error, usually in DNS, and asked your server to retry.
- Cisco Secure Email
- Provider
- Temporary (4xx)
- Class
- Sources checked
- Author
At a glance
- Code
- 451 4.4.3
- 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 4.4.3 #4.4.3 Temporary error occurred during SPF verification
What it means
In SPF, a temporary error means the check could not be finished, most often because a DNS lookup for the record, or for something it includes, timed out or failed. Cisco Secure Email Gateway answers that result with this default temporary reply when the administrator has chosen to reject it. Your server keeps the message and retries. A single occurrence is usually a passing DNS problem. If it keeps happening, look at the DNS servers for your domain and for every domain your SPF record includes.
Common causes
- The DNS servers for your domain answered slowly or not at all.
- A domain included in your SPF record has failing or unreachable DNS.
- A temporary DNS problem on the receiving side.
How to fix it
- 01Let your server retry the message.
- 02Query your SPF record and every include from more than one network to check they answer quickly.
- 03Remove includes for services you no longer use, and fix or replace slow DNS hosting.
Sources
What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.
Related codes
- 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.
- 550 5.7.1SPF check failed.The recipient’s Cisco Secure Email gateway checked SPF, found your server not authorised for the sender domain, and its policy rejects that result.
Further reading
All 7 Cisco Secure Email codesEvery code in the wikiPaste your own bounce