5.4.7SMTP 5.4.7: Titan recipient-domain quota exceeded

The RFC 3463 sample for the X.4.7 pattern is “Delivery time expired”, and RFC 5248 records that the associated basic status code list is not exclusive; the registry mirror used here holds no confirmed class entry for that pattern. This page therefore describes Titan Email behaviour as recorded in the accepted responses, which are the only exact 5.4.7 evidence accepted here, rather than a general definition of the code.

The two accepted responses name a quota on mail arriving for the recipient's domain, in an hourly variant and a daily variant. The scope is the whole domain and not one mailbox, and the response itself shows this three ways: the reason text names “Recipients Domain”, the reply is returned at the RCPT TO stage before any message data is offered, and the address in the response is only the address that transaction was for. The two variants differ in the accounting period the quota is measured over and not in the verdict, and neither response states the numeric limit, when the period began, or when it resets. This records a shared inbound quota at that provider, not a general definition of 5.4.7 and not a finding about the mailbox address.

The 550 reply permanently rejected the recorded transaction, and a sending system must not requeue that transaction to be offered again on a timer. The reply settles that one attempt and nothing more, and it reports a condition on the receiving side that can change without the sender doing anything. The accepted responses for this code were recorded before the message data was offered, so those replies evaluated neither the message nor the mailbox.

Class

Permanent failure

Retry

Do not retry unchanged

Suppression

Check the full context

Do not retry this transaction. A retry is the same queued message re-offered by the same queue on a timer with nothing changed, and the verdict already returned applies to it. A later attempt is a new transaction only when an operator decides to send it after the condition named in the response is reported changed by the side that controls it, which means the recipient domain's administrator or Titan confirming that the quota was raised or reset or that the named accounting period has passed. Elapsed time on its own is a weaker basis, because neither response states the limit in force or the reset point, so a send timed by estimate can return the same reply. Reaching the same person at a different domain is a different route rather than a retry of this transaction.

Do not suppress the recipient address on 5.4.7 alone. In the accepted responses the wording “Recipient address rejected” records where the rejection landed in the transaction, not what was evaluated: the reason those responses state is a quota shared by the entire recipient domain, so they carry no finding that the mailbox is unknown, closed, or invalid. Suppression needs evidence about the address itself, from a different code or from a later response.

• The recipient's Titan-hosted domain exceeded the hourly quota for incoming mail, which is the shorter of the two accounting periods the accepted responses name.
• The recipient's Titan-hosted domain exceeded the daily quota for incoming mail, the longer of the two periods named, so waiting out an hour is not a stated basis for expecting a different result.

1. Confirm the exact enhanced code and the basic reply paired with it, which in the accepted evidence is 550, and record whether the reason names the hourly or the daily variant.
2. Identify the receiving system that applied the condition and retain the evidence packet: the full response line verbatim, the recipient address and its domain, the date and time with UTC offset, the connecting IP address and envelope sender, and the sending system's queue identifier for the attempt.
3. Read the full response rather than the digits to separate the candidates, correlating rejections by recipient domain and time window to establish whether the whole domain or a single recipient is affected, and confirming that other destinations accepted mail in the same period.
4. State the single condition that authorises a new send, which is confirmation from the recipient domain's administrator or from Titan that the quota was raised or reset or that the named accounting period has passed.