554: rejected for a malicious QR code
Mimecast read a QR code in your message, followed the link inside it and judged that link malicious, so the message was rejected.
- Mimecast
- Provider
- Permanent (5xx)
- Class
- Sources checked
- Author
At a glance
- Code
- 554
- Provider
- Mimecast
- Temporary or permanent
- PermanentRefused for good: the message comes back to the sender, and resending it gets the same answer.
- Who has to act
- Either side, depending on the cause. Start with the checks below that are yours.
- What the server says
554 Malicious QR Code Detection
What it means
Mimecast’s URL protection extracts the address encoded in QR codes and scans it like any other link. When the result is malicious, the message is refused permanently with the security policies reply and this reason. QR codes are used in phishing because they hide the destination from the reader, so gateways treat them with suspicion. If your code is legitimate, the link may point to a domain or redirect chain with a poor reputation. Mimecast’s documented remedy for a false positive is for the customer to add the link to its Managed URLs as permitted.
Common causes
- The QR code points to a URL or domain that is flagged as malicious.
- The code leads through a redirect or link shortener that is associated with abuse.
- A false positive on a legitimate link.
How to fix it
- 01Decode the QR code yourself and check where it really leads, including any redirects.
- 02Replace it with a plain link to your own domain, or drop it.
- 03If the link is legitimate, ask the recipient’s IT team to add it as a permitted URL in Mimecast.
Sources
What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.
- Policies - Mimecast SMTP Error Codes (Mimecast support)mimecastsupport.zendesk.com
Related codes
- 554Transaction failed.The server permanently refused the transaction, often after receiving the message data or straight away when the connection opened.
- 554Rejected as spam or a virus.Mimecast’s scanning found a virus signature or gave the message a spam score above the maximum, so the recipient’s gateway refused it.
554 at other providers
- 554Permanent rejection (554).Yahoo or AOL rejected the message for good with a 554. Yahoo uses this code for several problems, from failed authentication to unacceptable content, so the wording of the reply tells you which.
- 554Failed authentication.Yahoo or AOL refused the message because it failed the checks that confirm the sending domain, such as DKIM against the domain's policy. Yahoo lists this among its permanent 553 and 554 errors.
- 554Recipient does not exist.The Yahoo or AOL account you wrote to does not exist. The failure is permanent: check the address with the recipient, and remove it from any list.
- 554No reverse DNS (PTR) record.Xfinity refused the connection because your sending IP has no PTR record. Every server sending to Xfinity needs valid reverse DNS, so the owner of the IP must add one.
- 554Rejected for breaking GMX guidelines.GMX refused the message permanently because the connection broke its guidelines. GMX points to its requirements page and asks for the full error message if the problem continues.
- 554IP address on the GMX blocklist.Your sending IP is on a blocklist that GMX manages itself, so its servers refuse the connection. GMX keeps a strict no tolerance policy toward spam.
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