Throttled Domains

Bandwidth and email throttling allow system administrators to limit the quantity of data that a SmarterMail mail server transmits and/or receives, in aggregate across an entire domain, within a specified period of time. This limit can be set by bandwidth, the number of emails transmitted, and/or by the number of bounced messages received. Domain-level throttling protects the server (and the domain's own sending reputation) from a domain as a whole flooding outbound mail — for example, several compromised mailboxes on the same domain sending spam simultaneously, where no single account trips its own per-user limit but the domain's combined traffic is clearly abnormal.

The Throttled Domains tab displays a list of every domain currently over one of its throttling limits. An entry here means the domain, in aggregate, has hit a limit within the current rolling window (per hour, by default) — it does not necessarily mean every user on the domain is misbehaving.

Note: Domain throttling limits are configured on the Domain Defaults template, found under Manage > Domains > Domain Defaults, and can be overridden for an individual domain from that domain's own Options settings.

The following details can be seen for each entry in the list:

Domain - The domain on the server that is currently being throttled.
Reason - The specific limit that was exceeded: Messages Out (too many outbound messages sent by the domain within the hour, combined across all of its users), Bandwidth Out (too much outbound data transmitted by the domain within the hour), or Bounces Received (too many bounce-back/NDR messages received by the domain within the hour — often an early sign that one or more accounts on the domain are sending to invalid addresses, such as a purchased or stale mailing list).
Date - The date and time the domain triggered the throttling action.

How Throttling Actually Behaves

Each domain throttle limit has its own configured action: Delay or Reject. By default, every throttle uses Delay, which means messages that exceed the limit are not deleted — they remain in the spool and are retried a short time later once the domain's usage for that rolling hour drops back under the threshold. If a system administrator changes a throttle's action to Reject instead, messages that exceed the limit are discarded outright rather than retried.

Throttled entries are not purely something an admin has to manually track down and clear: SmarterMail automatically re-checks each throttled domain every 60 seconds and removes the entry from this list on its own as soon as the domain's usage falls back under the configured limit — typically once the hourly counter rolls over.

Removing a Throttle

To immediately restore normal sending for a domain without waiting for the hourly counter to reset on its own, select one or more entries in the list and click Remove Throttle. This resets the domain's throttle counters right away, so mail from that domain can flow normally again immediately. This is useful once the root cause has been identified and resolved — for example, after disabling a compromised mailbox that was driving the domain's outbound volume, there's no need to wait out the rest of the hour for the domain-wide throttle to clear on its own.