Throttled Users

Bandwidth and email throttling allow system administrators to limit the quantity of data that a SmarterMail mail server transmits within a specified period of time. This limit can be set by the amount of outgoing bandwidth used, the number of outgoing emails sent, or the number of bounced messages received for a mailbox. Throttling exists to protect the server (and the server's overall sending reputation) from a single compromised or misconfigured account flooding outbound mail — for example, a mailbox whose password was guessed and is now being used to blast spam through the server's own SMTP connection.

The Throttled Users tab displays a list of every user currently over one of the throttling limits configured for their account. An entry here means the user has hit a limit within the current rolling window (per hour, by default), not that something is permanently wrong with the account.

Note: User throttling limits are configured on the User Defaults template, found under Manage > Domains > User Defaults (and by extension, on the Domain Defaults template that new domains inherit from). Domain administrators can further override these limits on a per-user basis from within their own domain's Accounts settings.

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

User - The email address of the user currently being throttled.
Mailing List - This acts as an indicator to specify whether the 'user' being throttled is actually a mailing list address rather than an individual mailbox.
Note: Mailing lists use their own, separate throttling limits (configured per list by the domain administrator) rather than the User Defaults limits used by individual mailboxes — a mailing list can only trigger the Messages Out or Bandwidth Out reasons, never Bounces Received.
Domain - The domain of the user that is currently being throttled.
Reason - The specific limit that was exceeded: Messages Out (too many outbound messages sent within the hour), Bandwidth Out (too much outbound data transmitted within the hour), or Bounces Received (too many bounce-back/NDR messages received within the hour — often a sign that the account is sending to a large number of invalid addresses).
Date - The date and time the user triggered the throttling action.

How Throttling Actually Behaves

Each 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 simply remain in the spool and are retried a short time later once the account'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 user every 60 seconds and removes the entry from this list on its own as soon as that user'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 user 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 account's throttle counters right away, so the user (or mailing list) can send again immediately. This is especially useful after confirming a flagged account wasn't actually compromised — for example, a marketing team member who legitimately sent a large one-time campaign and tripped the Messages Out limit.