Gmail 552 5.7.0
Message content
The provider rejected something inside the message, such as an attachment, link, or security-sensitive content.
Decision
Do not retry unchanged. Fix the sender setup first.
Confidence: high. Recipient validity: unknown.
Match this reply
- SMTP stage
- End of DATA
- Endpoint
- Inbound MX
security issueblockedattachmentStart here
- 1
Remove blocked attachments, suspicious links, or executable content from the message.
- 2
Send a small test message to confirm the rejection is content-related before retrying the full campaign.
Confirm the cause
- Remove suspicious links, blocked attachments, executable files, or high-risk URL redirects.
- Send a plain-text or minimal HTML test to confirm the rejection is content-related.
- Reintroduce content in small changes so the blocked element is easy to identify.
App handling
- Treat this as a sender setup incident, not a bad recipient.
- Hold similar mail for the same sender domain or provider until the fix is verified.
- Retry after a fresh single-recipient test succeeds.
Avoid
- Do not retry unchanged in a loop.
- Do not suppress the recipient unless the text explicitly says the mailbox is invalid.
- Do not treat a permanent SMTP code as proof that the address is bad; policy and routing failures can also be permanent.
Common causes
- An attachment, link, URL reputation signal, or executable payload triggered filtering.
- The message resembles phishing, malware, or high-risk bulk mail.
- The provider blocks this content type for the recipient or sending route.
Developer details
Fields to log
raw SMTP replyremote MX or hostSMTP stagereply codeenhanced codeprovidermatched rule idrecipientsending domaindecisiontimestamp
Classifier evidence
- Specific cause
- blocked attachment or security content
- Evidence
- official