554: rejected 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.
- 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 Email rejected due to security policies.
What it means
This is Mimecast’s permanent rejection after scanning the message itself. The reason line (MCSpamSignature) points to either a virus signature or a spam score over the highest threshold. The score is not shown, even to the customer’s administrators. Mimecast’s advice to senders who are not its customers is to ask the recipient to adjust their configuration and permit your address. Anti-spam checks can be bypassed with a Permitted Senders or Auto Allow policy, while anti-virus checks cannot be bypassed at all. A message that really carries malware has to be cleaned before it will get through.
Common causes
- The message content, links or sending pattern scored as spam, which is common with cold outreach templates sent at volume.
- An attachment matched a virus signature.
- Links in the message point to domains with a poor reputation.
How to fix it
- 01Scan any attachment and remove it if in doubt; send a link to a reputable host instead.
- 02Rewrite the message plainly: fewer links, no link shorteners, no tracking-heavy templates.
- 03Check your sending IP and link domains on blocklists.
- 04Ask the recipient to have their IT team add a Permitted Senders or Auto Allow policy for your address; this covers spam checks only.
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 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.
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.
Further reading
All 19 Mimecast codesEvery code in the wikiPaste your own bounce