>>> [!note] Migrated issue <!-- Drupal.org comment --> <!-- Migrated from issue #3477699. --> Reported by: [lussoluca](https://www.drupal.org/user/138068) Related to !41 >>> <h3 id="summary-problem-motivation">Motivation</h3> <p>Sometimes, only one instance of a message must be present in a transport at a time.</p> <h3 id="summary-proposed-resolution">Proposed resolution</h3> <p>Implement something like: <a href="https://github.com/symfony/symfony/issues/54126">https://github.com/symfony/symfony/issues/54126</a>.</p> <h3 id="summary-remaining-tasks">Remaining tasks</h3> <p>Implement/test</p> <h3 id="summary-ui-changes">User interface changes</h3> <p>None</p> <h3 id="summary-api-changes">API changes</h3> <p>A new Stamp will be added to flag a message to be unique</p> <h3 id="summary-data-model-changes">Data model changes</h3> <p>None</p>