SMTP code 552 is a permanent rejection indicating that the message cannot be stored because it exceeds a size limit. This can mean the individual message is too large for the server (exceeding the SIZE parameter advertised in EHLO), the recipient's mailbox has reached its permanent storage quota, or the message plus attachments exceeds an administrator-configured maximum. Unlike 452 (temporary storage issue), 552 is permanent — the sender cannot resolve this by simply retrying. The message must be made smaller, or the recipient must free space in their mailbox.
Most mail servers enforce a maximum message size (often 10-50 MB). The server advertises this in its EHLO response via the SIZE extension. If the message exceeds this limit, it is rejected with 552 during or after the DATA phase.
The recipient's mailbox has reached its hard storage quota and the server treats this as a permanent failure. This is different from 452 (temporary) — the server has determined the condition requires the recipient to take action.
Some servers reject messages with oversized attachments or certain attachment types (e.g., .exe, .zip) regardless of the total message size. The rejection happens during content filtering after the DATA phase.
Send EHLO and look for the SIZE extension. This tells you the maximum message size in bytes that the server will accept.
openssl s_client -connect mail.example.com:25 -starttls smtp
Compress attachments, use a file-sharing service instead of email attachments, or split the message into smaller parts. Remember that base64 encoding (used for attachments) increases size by approximately 33%.
If the rejection mentions quota, the recipient needs to delete messages to free space. Contact them through an alternative channel.
The server does not have enough storage to process the command. The sender should retry later when space may be available.
The entire mail transaction has failed. Used as a catch-all permanent rejection, often appearing at connection time.
The recipient's mailbox does not exist, or the server has permanently rejected the message due to policy.