552 5.3.4 / 5.2.3 error: Message too large
The message, with attachments and encoding overhead, is bigger than the recipient's server accepts.
How to fix 552 5.3.4 / 5.2.3
- Remove or shrink attachments; for cold email, send a link instead of a file.
- Remember that attachments grow about a third when encoded.
Why this happens
Content filters score wording, links, images and HTML structure, and many also check each domain in the message against reputation lists. A single link-shortener or a tracking domain with a bad history can sink an otherwise clean email.
How to keep it from coming back
Write plain, relevant copy, use your own domain for links instead of shared shorteners, include a plain-text part, and test the exact message before a campaign rather than only the template.
Should I retry a 552 5.3.4 / 5.2.3 error?
Not as it stands. A permanent error means the same message will be refused again until the cause is fixed on your side. Fix the cause first, then send a fresh message; if it keeps failing after that, check the full text of the bounce for the exact reason.
Got the full bounce message?
The text after the code names the exact reason, and the same code can mean different things at different receivers. Paste the whole message into the decoder - it runs in your browser and nothing is sent.
Open the bounce decoderRelated error codes
Seeing this again and again? That's usually a reputation or authentication problem we can trace and fix at the source.
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