6 files declare their use of IdentityChannelManagerInterface in Courier 8

ComposeAccessCheck.php in courier_message_composer/src/Access/ComposeAccessCheck.php

CourierMessageController.php in courier_message_composer/src/Controller/CourierMessageController.php

MessageForm.php in courier_message_composer/src/Form/MessageForm.php

Permissions.php in courier_message_composer/src/Permissions.php

Settings.php in src/Form/Settings.php

TemplateEditForm.php in src/Form/TemplateEditForm.php