552 5.3.4 "Message Size Exceeds Fixed Limit": What It Means and How to Fix It
552 5.3.4 means the receiving server refused the message because it is too big. Gmail's wording is "Your message exceeded Google's message size limits." Other servers say "Message size exceeds fixed limit." The address is fine. Shrink the message and send it again to the same person.
The 552 5.3.4 code page has the short version. This post covers the reasoning.
How the code is built
SMTP codes have a three-digit reply and an enhanced status code defined in RFC 3463, written class.subject.detail:
| Part | Value | Meaning |
|---|---|---|
| Reply code | 552 | Requested mail action aborted, exceeded storage allocation |
| Class | 5 | Permanent failure |
| Subject | 3 | Mail system status |
| Detail | 4 | Message too big for system |
The first digit of 5 makes it permanent for that message. See hard bounce vs soft bounce for how senders treat the classes.
What makes a message too big
- Attachments. Binary files are encoded for email, which makes them roughly a third larger in transit than on disk. A file that looks under the limit can still fail.
- Embedded images. Large images pasted into the HTML body count towards the size.
- Headers. Long forwarding chains can grow the headers.
The limit belongs to the receiving server, and it is not always the same as yours.
What to do
- Do not remove the recipient. Nothing is wrong with the address.
- Replace attachments with a link to the file in a shared drive or your own site.
- Compress or resize images, and host them instead of embedding them.
- Resend the smaller message. Test with one recipient first if the bounce came from a campaign.
- Check your tool's behaviour. Some sending tools count every bounce as a hard bounce and suppress the address. Release it again if yours did; see release a hard bounce from suppression.
For campaigns, keep attachments out of cold and bulk mail entirely. A link is smaller, loads faster and does not hit this limit. The smtp transcript explainer reads a pasted bounce and explains each line.
Can verification prevent it
No. 5.3.4 is about message size, so list verification does not change it, and the address should not be suppressed. What it does protect is the rest of your sending: a clean list keeps your bounce rate low so that an occasional size bounce does not stand out.
Keep the address side clean
This code does not come from your list, but every bounce still counts against your sending reputation, so the addresses you do send to should be real. Upload your list on the verify page: the first 100 email checks are free with a Google sign-in, no card. Each address comes back valid, risky or invalid with a reason such as "Mailbox not found" or "Accepts all addresses", and nothing is sent to anyone on the list. For larger or recurring lists, see bulk email verification, list cleaning and pricing.
Common questions
What does 552 5.3.4 mean?
The message is larger than the receiving server accepts. RFC 3463 defines X.3.4 as message too big for system. Gmail words it as Your message exceeded Google's message size limits.
Is 552 5.3.4 a hard bounce?
It is a permanent failure for that message as sent, but the address is fine. Make the message smaller and resend it to the same recipient.
Why is my attachment too big when it is under the limit on disk?
Attachments are encoded for transit, which makes them roughly a third larger than the file on disk, so a file near the limit can fail.
Should I remove the address from my list?
No. The rejection is about the message, not the mailbox, and list verification does not change it.
Check your list before you send
Real mailbox checks over SMTP, and nothing is sent to the address. Sign in with Google and your first 100 email checks are free, no card. Plans for bigger lists are on the pricing page.