Gmail and Google Workspace · permanent error
552 5.3.4: subject line too long
Gmail rejected the message because its Subject header is longer than Google's header size limits allow.
- Gmail
- Provider
- Permanent (5xx)
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- Sources checked
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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 Your message has a Subject: header that exceeds Google's message header size limits.
What it means
The subject line is too long for Gmail. People rarely type a subject anywhere near that long, so the cause is usually software: a template that inserts a whole field or list into the subject, a step that appends to it on every forward or retry, or non-ASCII text encoded several times over. Google links the reply to its page on Gmail message header limits. Shorten the subject and send again; inboxes only show the start of a subject anyway.
Common causes
- A template that inserts long data, such as a full record or list, into the subject.
- Code that appends to the subject repeatedly, for example on each forward or retry.
- Repeated encoding of non-ASCII text, which multiplies its length.
How to fix it
- 01Check the Subject header of the rejected message as it was sent.
- 02Limit the subject length in your template or code.
- 03Fix any step that appends to or re-encodes the subject.
- 04Resend with a short subject.
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.
- 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
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