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Using the kcli Command-Line Client

KumoMTA comes with several API endpoints to make administration of the server easier for common tasks, and additionally comes with the kcli command-line client which provides access to the APIs for local administrative tasks.

The kcli client is located at /opt/kumomta/sbin/kcli and requires a configured HTTP Listener to function.

At minimum, the kcli client must be passed an endpoint and a command:

$ kcli --endpoint bounce-list

The --endpoint parameter indicates the HTTP API endpoint you have configured for your KumoMTA instance. This documentation uses because that endpoint is shown as a suggested default for that http listener. You need to adjust it to match whatever you have configured for your HTTP listener in your environment.

Since: Version 2023.08.22-4d895015

The functionality described in this outlined box requires version 2023.08.22-4d895015 of KumoMTA, or a more recent version.

The --endpoint defaults to and can be omitted. If KUMO_KCLI_ENDPOINT is set in the environment, its value will be used if --endpoint is not specified.

In earlier versions, you need to explicitly pass --endpoint.

Monitoring Queue Status

The kcli client can be used to report on messages currently queued in the server with the following format:

$ kcli --endpoint queue-summary
SITE                                              SOURCE       PROTO       D T C   Q
(alt1|alt2|alt3|alt4)? hdfc.s-ip102 smtp_client 0 0 5 995
(alt1|alt2|alt3|alt4)? hdfc.s-ip103 smtp_client 0 0 5 995


This output format is subject to change and is not suitable for a machine to parse. It is expressly unstable and you must not depend upon it in automation.

The data behind this output is pulled from the metrics.json endpoint, which is machine readable.

The output is presented in two sections:

  1. The ready queues
  2. The scheduled queues

The ready queue data is presented in columns that are mostly self explanatory, but the numeric counts are labelled with single character labels:

  • D - the total number of delivered messages
  • T - the total number of transiently failed messages
  • C - the number of open connections
  • Q - the number of ready messages in the queue

Note that the ready queue counter values reset whenever the ready queue is reaped, which occurs within a few minutes of the ready queue being idle, so those numbers are only useful to get a sense of recent/current activity. Accurate accounting must be performed using the delivery logs and not via this utility.

The scheduled queue data is presented in two columns; the queue name and the number of messages in that queue.

Managing Bounces

Bouncing Messages

The kcli client can be used to administratively bounce messages currently queued in the server with the following format:

$ kcli --endpoint bounce --everything --reason purge
  "id": "0234c7c9-afd3-49f9-9a4c-a1cc37fcc53b",
  "bounced": {},
  "total_bounced": 0

Allowed arguments for the bounce command include:


Optional string. The domain name to match. If omitted, any domain will match.


Optional string. The campaign name to match. If omitted, any campaign will match.


Optional string. The tenant to match. If omitted, any tenant will match.


If you specify none of domain, campaign or tenant, then ALL queues will be bounced.

With great power, comes great responsibility!


Required. Reason to log in the delivery log.


Optional duration string. Defaults to "5m". Specifies how long this bounce directive remains active.

While active, newly injected messages that match the bounce criteria will also be bounced.

See the Bounce API page of the Reference Manual for more information.

Listing Current Bounces

You can list the currently active bounce commands with the following command:

$ kcli --endpoint bounce-list
    "id": "169c3dc0-6518-41ef-bfbb-1f0ae426cb32",
    "campaign": null,
    "tenant": null,
    "domain": null,
    "reason": "purge",
    "duration": "4m 50s 207ms 320us 231ns",
    "bounced": {
      "": 1
    "total_bounced": 1

See the Admin Bounce List API page of the Reference Manual for more information.

Removing a Bounce

Because bounce commands default to a five-minute duration, messages will continue to bounce after the command has been issued. This helps with scenarios such as when a campaign needs to be aborted, but the entire campaign may not have been injected at the time the command was issued.

Sometimes after a bounce has been issued there is a need to cancel the bounce before the time window has expired. Once a bounce command's ID is determined with the bounce-list command, the bounce can be canceled with the bounce-cancel command:

$ kcli --endpoint bounce-cancel --id 169c3dc0-6518-41ef-bfbb-1f0ae426cb32
removed 0234c7c9-afd3-49f9-9a4c-a1cc37fcc53b

See the Bounce Cancel API page of the Reference Manual for more information.

Managing Suspensions

Setting The Diagnostic Log Level

While the log level is typically set in your configuration, it can also be set on an ad-hoc basis using the set-log-filter command in kcli:

$ kcli --endpoint set-log-filter 'kumod=trace'

See the Set Diagnostic Log Filter page of the Reference Manual for more information.

Monitoring inbound SMTP handshaking

When debugging, it is often helpful to monitor the full SMTP handshaking process in real-time. The kcli client enables that for inbound connections with the trace-smtp-server function:

$ kcli trace-smtp-server