SMTP code 452 means the receiving mail server has run out of storage space and cannot accept additional messages. This can refer to the mail spool partition being full, the recipient's individual mailbox quota being exceeded, or the server's temp directory having no free space for processing. Unlike 552 (which is a permanent rejection for a message that is too large), 452 is temporary — the condition may resolve when old messages are deleted, quotas are increased, or disk space is freed. The sending MTA should queue the message and retry on its normal schedule.
The disk partition where the mail server stores queued and delivered messages has reached capacity. No new messages can be written until space is freed. This is a server-wide issue affecting all recipients on that server.
The individual recipient's mailbox has reached its storage quota. The server returns 452 because the condition is temporary — the recipient can delete messages to free space. Some servers return 552 instead for quota issues, but 452 is more correct since it is recoverable.
Some servers return 452 when the number of RCPT TO commands in a single message exceeds the server's per-transaction limit. The remaining recipients should be sent in a separate transaction.
452 is temporary. The sending MTA should automatically retry. The condition typically resolves when the recipient deletes messages, the administrator frees disk space, or quota resets occur.
If the recipient's mailbox is full, they may not be aware. Contact them through an alternative channel and let them know their mailbox needs to be cleaned up.
If sending to many recipients in one transaction, split them into batches. The server's EHLO response may advertise a maximum recipient count.
openssl s_client -connect mail.example.com:25 -starttls smtp
If you administer the receiving server, check disk usage on the mail spool partition and the server's queue directory.
df -h /var/spool/mail
The server encountered an internal error while processing the command. The message should be retried later.
The message was rejected because it exceeds the recipient's storage limit or the server's message size limit.
The recipient's mailbox does not exist, or the server has permanently rejected the message due to policy.