5.4.7Recipient domain's inbound rate quota exceeded (Titan Email)

A different condition than the registry sample sits behind concrete code 5.4.7: the Titan Email responses below cover the recipient domain's mail-acceptance rate quota being exceeded, not delivery-time expiry, and that production evidence alone records the code here. Code 5.4.7 pins a permanent class onto registry pattern X.4.7, but X.4.7 itself stays unresolved for every class in this catalog. The registry's sample text is "Delivery time expired": a message judged too old after it outran its queue time or its sender-specified TTL. Because the registry's Associated Basic Status Code is "Not given", that sample does not mechanically confirm any basic SMTP code or class.

Documented Titan Email behavior supplies the concrete code 5.4.7 described here. A recipient domain hosted on that service has exceeded an administrative limit on how many messages it accepts in an hourly or daily window, and Titan rejects further messages until the window clears. That uses code number 5.4.7 for a rate-quota condition, not for the delivery-time expiry named in the registry's sample text. RFC 3463 Section 3.4 defines the X.4 "Network and Routing Status" subject class for network- and routing-related failures. RFC 3463's table gives the X.4.7 pattern the sample text "Delivery time expired" and explains that the message was considered too old because it lingered on the rejecting host too long or exceeded the sender's specified time-to-live. The Associated Basic Status Code there is "Not given", so the registry attaches this pattern to no specific basic SMTP code. RFC 5248 confirms that the Associated Basic Status Code list is illustrative rather than exclusive, yet it adds no further class confirmation here. In this catalog the registry mirror marks X.4.7 unresolved for every class: no confirmed entry exists, matching the evidentiary gap for other unconfirmed detail codes in this catalog.

The leading digit 5 denotes a permanent failure: Titan returns this response as a permanent rejection of this specific delivery attempt (basic code 550), not as a 4xx deferral. This does not mean the recipient domain is blocked outright — the limit is tied to a time window (hour or day) and may clear once that window resets. Treat this specific attempt as failed, and a later send to this domain as a new attempt, not as an automatic retry of the same SMTP transaction.

Class

Permanent failure

Retry

Do not retry unchanged

Suppression

Check the full context

Do not let your MTA auto-retry this same delivery attempt at short intervals — the class-5 code signals a permanent rejection of this transaction. If the message matters, consider a manual resend after a reasonable interval (longer than the typical hourly or daily window, depending on which variant occurred), treating it as a new delivery attempt. Do not treat a single 5.4.7 as grounds to give up on this domain permanently.

Do not suppress the recipient address based on code 5.4.7 alone: the condition is a rate quota on the recipient domain's mail acceptance as a whole, hosted on Titan Email, not the validity of this particular address or the state of one mailbox. Suppression decisions should follow independent, address-specific signals (hard bounces, addressing codes) rather than this shared, domain-level limit.

• The recipient domain, hosted on Titan Email, is on a plan with a cap on the number of messages it accepts within an hourly or daily window, and current inbound volume (from this and other senders combined) has exceeded that cap.
• A sudden spike in mail sent to this domain in a short period (a campaign, a mailing list, or many senders at once) exhausted the available quota faster than usual.
• The accepted Titan examples' descriptions link directly to the provider's documentation on sending/receiving rate limits and on incoming mail reject codes — documented behavior of this specific provider, not a general definition of code 5.4.7 across providers.

1. Inspect the raw SMTP response and confirm the enhanced code is exactly 5.4.7, with a basic reply in the 5xx class (550 in the accepted examples); note whether the text names the hourly or the daily quota variant.
2. Correlate the response with the specific message, recipient address, and exact attempt time — needed to judge when the relevant window (hour or day) might have reset.
3. If you send to multiple recipients on the same Titan-hosted domain, check whether similar 5.4.7 rejections occur for other addresses in the same time window — a sign of a domain-wide limit rather than a single address's problem.
4. Where possible, contact the recipient domain's administrator (or ask the recipient to do so) about the domain's current Titan Email plan and rate quota.