Message too big for system
Production Risk
Low — affects only unusually large messages.
The message is too large to be processed by the receiving mail system. Unlike 5.2.3 which reflects an administrative limit, 5.3.4 indicates the message exceeds a hard system capability boundary.
- 1The message exceeds the MTA's absolute maximum processable size.
- 2A transient resource constraint on the mail system is preventing processing of large messages.
- 3The message queue or spool storage is insufficient to hold the message.
Sending an extremely large message that the receiving mail system cannot physically process or store.
DATA # After transmitting large message body: 552 5.3.4 Message too large
expected output
552 5.3.4 ...
Fix
Reduce message size before sending
WHEN When sending messages with large payloads
# Strip and re-attach large files via external storage
# Maximum recommended email attachment size: 10 MB
# For larger files, use a pre-signed URL:
const url = await s3.getSignedUrl('getObject', { Bucket, Key, Expires: 86400 });
// Include url in email body instead of attachmentWhy this works
Moving large payloads out of the message body and referencing them via URLs is the standard approach for large content delivery.
✕ Retry the same message unchanged
System size limits are hard boundaries; the message must be reduced in size.
RFC 3463 — Enhanced Mail System Status Codes
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