Enhanced SMTP status code · RFC 3463 · IANA

5.3.4 Message too big for the system

The message exceeds the server's size limit.

Class: Permanent failure
Class 5: a permanent failure. Resending the same message will not help: something about the message, the sender or the destination must change (RFC 3463 §3.1). The registry says this code is only useful as a permanent failure.
Subject: X.3 · Mail system
Something about the destination server; under its administrator's control.
Associated basic codes (IANA registry)
552554
Source
RFC 3463 · IANA

How 5.3.4 appears at providers

The exact text from the provider's documentation, as you see it in the bounce, and what it means.

Gmail

552 5.3.4Your message exceeded Google's message size limits.

The message exceeds Gmail's limits: total size, number of attachments, or the size of the header or of one field in it. Make the message or header smaller.
552 5.3.4The number of attachments (num-attachments) exceeds Google's limit of limit attachments.

The message exceeds Gmail's limits: total size, number of attachments, or the size of the header or of one field in it. Make the message or header smaller.
552 5.3.4The size of your message (size bytes) exceeded Google's message size limits of limit bytes.

The message exceeds Gmail's limits: total size, number of attachments, or the size of the header or of one field in it. Make the message or header smaller.
552 5.3.4Your message exceeded Google's message header size limits.

The message exceeds Gmail's limits: total size, number of attachments, or the size of the header or of one field in it. Make the message or header smaller.
552 5.3.4Your message exceeded Google's message header size limits. Messages must not exceed limit total header bytes or limit header fields.

The message exceeds Gmail's limits: total size, number of attachments, or the size of the header or of one field in it. Make the message or header smaller.
552 5.3.4The size of the header name header value (size bytes) exceeds Google's limit of limit bytes per individual header size.

The message exceeds Gmail's limits: total size, number of attachments, or the size of the header or of one field in it. Make the message or header smaller.
552 5.3.4The size of one of the header values (size bytes) exceeds Google's limit of limit bytes per individual header size.

The message exceeds Gmail's limits: total size, number of attachments, or the size of the header or of one field in it. Make the message or header smaller.
552 5.3.4The size of a header name (size bytes) exceeds Google's header name limit of limit bytes.

The message exceeds Gmail's limits: total size, number of attachments, or the size of the header or of one field in it. Make the message or header smaller.
552 5.3.4Your message has a Subject: header that exceeds Google's message header size limits.

The message exceeds Gmail's limits: total size, number of attachments, or the size of the header or of one field in it. Make the message or header smaller.

Have the whole error message?

Sources: RFC 5321 · RFC 3463 · RFC 3464 · IANA · Gmail · Microsoft 365 · read on 26 September 2026