5.3.4 SMTP bounce: message too big for system

What 5.3.4 means

The message exceeds the receiving system's maximum message size.

Message text

Message too big for system

Common causes of 5.3.4

• Message including attachments is over the receiver's size limit

How to fix 5.3.4

1. Reduce message size or send attachments via a link.
2. Check the receiver's published size limit with the recipient.

Check your domain

Read the headers of a bounced messageRuns in your browser; nothing is uploaded.

Have the full bounce message? Paste it into the bounce code lookup and it will match the code and the provider for you. Open the bounce code lookup.

How to read 5.3.4

The second part, 5.3.4, is an enhanced status code (RFC 3463 §2) written class.subject.detail. Class 5 is a Permanent failure (5xx): the command was rejected and the sender should not repeat it unchanged (RFC 5321 §4.2.1; RFC 3463 §2).. Subject 3 is mail system: a problem with the receiving system as a whole. The detail number refines the subject, and providers may define details of their own, which is why one code can read differently at Gmail, Microsoft and Yahoo.

Do not keep resending the same message: a permanent failure repeats until the cause is fixed. Correct the cause, then send a new message.

Official source: www.rfc-editor.org. Last verified 2026-10-20.

Related guides

• How to create an SPF record (syntax and examples)
• How DKIM works and how to publish a DKIM record
• How to set up a DMARC record, from p=none to p=reject

Related codes

• 550 SMTP: mailbox unavailable
• 551 SMTP: user not local
• 552 SMTP: storage exceeded
• 553 SMTP: mailbox name not allowed
• 554 SMTP: transaction failed
• 5.1.1 SMTP: bad destination mailbox

FAQ

All bounce codes