SMTP 552: message too large or recipient mailbox full
What 552 5.3.4 ("Message size exceeds fixed maximum message size") and 552 5.2.2 ("Mailbox full", "Quota exceeded") mean, the size limits of Gmail, Outlook, Yahoo and relays, and how to handle attachments and full mailboxes.
What 552 means: The server refused the message because of a size or storage limit — either yours is too big for their maximum, or the recipient's mailbox has no room.
Causes, most likely first — and the fix for each
- 552 5.3.4 — the message (after base64 encoding, ~35% bigger than the files) exceeds the receiver's or relay's limit (Gmail 25 MB receive, Outlook ~20–25 MB, many corporate servers 10 MB, QueenSMTP 25 MB).
Fix: Compress or split attachments, or send a download link instead of the file. - 552 5.2.2 "Mailbox full" / "Quota exceeded" / "Over quota" — the recipient is out of space.
Fix: Nothing on your side; treat as a soft bounce and retry in a day or two. It is not a spam or authentication signal. - Your own MTA's message_size_limit (Postfix default 10 MB).
Fix: Raise message_size_limit in main.cf if you really must send large files.
How to confirm which one you have
Look at the full reply: 5.3.4 = your size; 5.2.2 = their quota.
Open the SMTP tester Check SPF / DKIM / DMARC
Still stuck? Use a relay that tells you why
QueenSMTP shows every message's exact server reply in the log, verifies your domain's SPF and DKIM before you send, and is not subject to mailbox-provider caps. $5/year plus $0.10 per 1,000 emails; 100 a day free to test.
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Questions about 552
25 MB for a message including encoded attachments; larger files should be shared as links (Drive).
No — it is a soft bounce. Retry later; only suppress the address after repeated failures.
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