SMTP 552 5.3.4
message too big
SMTP 552 5.3.4 means the message is larger than the receiving server accepts. RFC 3463 defines X.3.4 as "message too big for system". Gmail returns it as "Your message exceeded Google's message size limits." The address is fine; the message needs to be smaller.
Should you remove the address?
Keep the address; fix the sending side
Keep it. The rejection is about the message, and the same address will accept a smaller one.
Block. Retrying changes nothing until the cause on your side is fixed.
How it appears
552 5.3.4 Your message exceeded Google's message size limits.
552 5.3.4 Message size exceeds fixed limit
What causes it
- Large attachments. Encoding makes an attachment roughly a third larger in transit than on disk.
- Large embedded images in the HTML body.
- Headers that grew too large, usually from long forwarding chains.
How to fix it
In order — try the first one first.
- Replace attachments with a link to the file.
- Compress or resize images, and host them instead of embedding them.
- Do not remove the recipient. Resend a smaller message.
Who sends it
Gmail documents several 5.3.4 variants for overall size, attachment count and header size. Every server has a size limit, and they differ.
Gmail
Reply text Your message exceeded Google's message size limits.
Gmail has separate 5.3.4 texts for too many attachments, oversized headers and a Subject line over the limit.
Common questions
- What does SMTP 552 5.3.4 mean?
- SMTP 552 5.3.4 means the message is larger than the receiving server accepts. RFC 3463 defines X.3.4 as "message too big for system". Gmail returns it as "Your message exceeded Google's message size limits." The address is fine; the message needs to be smaller.
- Should I retry a 552 5.3.4 error?
- No. 552 is a permanent failure, so the message will never be delivered no matter how many times you try. Remove the address — repeated sends to permanent failures are one of the main signals mailbox providers use to throttle a sender.
- How do I fix SMTP 552 5.3.4?
- Replace attachments with a link to the file.
- Is 552 5.3.4 a hard bounce or a soft bounce?
- 552 5.3.4 is a block rather than a classic hard or soft bounce. The rejection is about your sending (authentication, reputation, content or the recipient's policy), not about whether the address exists. Retrying changes nothing until the cause on your side is fixed.
- Should I remove the address after a 552 5.3.4 bounce?
- Keep it. The rejection is about the message, and the same address will accept a smaller one.
- Will verifying my list prevent 552 5.3.4?
- No. Size limits are about the message, so verification has nothing to add here.
Clean the list before the next send.
A bounce report only tells you about the addresses you already mailed. The rest of the list has the same kinds of dead mailboxes in it, and each one becomes a hard bounce recorded against your domain the moment you send.
- A real SMTP mailbox check on every row, before anything is sent
- Dead and mistyped addresses split out, so they never reach your sending tool
- Catch-all, disposable and role addresses flagged alongside
Plans from $9 a month, cancel anytime, no contract. Sign in with Google and your first 100 email checks are free, no card. The free tools stay free either way.
Other 552 replies
Sources
- Source: Google Workspace Admin Help: Gmail SMTP errors and codes
- Source: RFC 3463: Enhanced Mail System Status Codes
Provider wording is quoted only where the provider publishes it.
Last reviewed 2026-10-22