5.3.4: message too big
The message is larger than the maximum size the receiving system accepts for any message, so it was refused and has to be made smaller.
- Standard
- Provider
- Permanent (5xx)
- Class
- Sources checked
- Author
At a glance
- Code
- 5.3.4
- Provider
- Standard SMTP codes
- Temporary or permanent
- PermanentRefused for good: the message comes back to the sender, and resending it gets the same answer.
- Who has to act
- The sender. The fix is on the sending side: your domain, your server or your list.
- What the server says
5.3.4 Message too big for system
What it means
X.3.4 is the system-wide size limit, as opposed to the per-mailbox limit of X.2.3. RFC 3463 says it is useful only as a permanent error, so 5.3.4 is what you see and the message is returned, often with reply code 552 or 554. Servers that support the SIZE extension (RFC 1870) announce their limit in the EHLO reply, so a sending server can refuse an oversized message before transferring it. Base64 encoding makes attachments roughly a third larger than the files on disk, which is easy to forget when checking against the limit.
Common causes
- Attachments that push the message over the receiver's limit.
- Base64 encoding, which makes attachments larger than the original files.
- A forwarding or relay server with a lower limit than the final destination.
How to fix it
- 01Make the message smaller: compress images or remove attachments.
- 02Share large files by link instead of attaching them.
- 03If you run the sending server, read the SIZE value in the receiver's EHLO reply to see its limit.
- 04Recipient admins: raise the message size limit if large messages are expected.
Sources
What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.
Related codes
- 552Storage allocation exceeded.The receiving server aborted the message because it exceeded a storage limit, usually a full mailbox or a message larger than allowed.
- 5.2.3Message too large for this mailbox.The message is bigger than the size limit set for this particular mailbox, which an administrator set lower than the system-wide limit.
- 552 5.7.16Too big for its priority.The server limits message size per priority level, and this message is larger than allowed for the priority it was sent with.
5.3.4 at other providers
- 552 5.3.4Message too large.The message, with its attachments, is larger than Gmail accepts, so it was rejected and needs to be made smaller or sent another way.
- 552 5.3.4Too many attachments.Gmail rejected the message because it carries more attachments than Google allows in one message, whatever their size.
- 552 5.3.4Message headers too large.Gmail rejected the message because its header section as a whole is larger than Google allows, or holds too many header fields.
- 552 5.3.4A single header is too large.Gmail rejected the message because one of its header fields holds a value longer than Google allows for a single header.
- 552 5.3.4Header name too long.Gmail rejected the message because the name of one of its header fields is longer than Google allows.
- 552 5.3.4Subject line too long.Gmail rejected the message because its Subject header is longer than Google's header size limits allow.
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