Gmail and Google Workspace · permanent error
552 5.3.4: A 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.
- Gmail
- Provider
- Permanent (5xx)
- Class
- Sources checked
- Author
At a glance
- Code
- 552 5.3.4
- Provider
- Gmail and Google Workspace
- 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
552 5.3.4 The size of one of the header values…per individual header size.
What it means
Besides the total size of the header section, Gmail limits each header field on its own. The bounce gives the size of the offending header, in one version its name as well, and Google's limit in bytes. Values that long usually come from software: a To or Cc line with a very large number of addresses, a References header that has grown over a long thread, or a custom header packed with encoded data. Shorten the value and send the message again.
Common causes
- A To or Cc header listing a very large number of addresses.
- A References or In-Reply-To header that has grown over a very long thread.
- A custom header holding large encoded data.
How to fix it
- 01Find the header the bounce names, or inspect the message with a header analyzer.
- 02Split large recipient lists, or use Bcc or a group address.
- 03Trim custom headers in the sending software, or move their data into the body.
- 04Start a new thread if References has grown too long.
Sources
What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.
- Gmail SMTP errors and codes (Google Workspace Admin Help)knowledge.workspace.google.com
Related codes
- 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 5.3.4Header name too long.Gmail rejected the message because the name of one of its header fields is longer than Google allows.
- 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.
- 5.3.4Message 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.
5.3.4 at other providers
Further reading
All 108 Gmail codesEvery code in the wikiPaste your own bounce