@Ingo_Richtsmeier after adding the camunda-engine-plugin-connect
dependency also the issue persists.
dependencies added for mail-connectors are:
compile group: 'org.camunda.bpm', name: 'camunda-engine-plugin-connect', version: '7.11.0'
compile group: 'org.camunda.connect', name: 'camunda-connect-connectors-all', version: '1.2.2'
compile group: 'org.camunda.connect', name: 'camunda-connect-core', version: '1.2.2'
compile group: 'org.camunda.bpm.extension', name: 'camunda-bpm-mail-core', version: '1.2.0'
compile group: 'com.sun.mail', name: 'javax.mail', version: '1.6.2'