7 files declare their use of SpoolStorageInterface in Simplenews 8

Mailer.php in src/Mail/Mailer.php

MailerInterface.php in src/Mail/MailerInterface.php

MailSettingsForm.php in src/Form/MailSettingsForm.php

NodeTabForm.php in src/Form/NodeTabForm.php

PendingSensorPlugin.php in src/Plugin/monitoring/SensorPlugin/PendingSensorPlugin.php

simplenews.drush.inc in ./simplenews.drush.inc

Drush commands for administer Simplenews.

SimplenewsSourceTest.php in src/Tests/SimplenewsSourceTest.php

Simplenews source test functions.