feat: email recipient whitelist

.env

@@ -70,6 +70,14 @@ APP_BPN_CRM_ID_TEAMER=1070
 APP_DEFAULT_EMAIL_FROM=[email protected]
 APP_DEFAULT_EMAIL_TO=[email protected]
 
+# Regular expressions of the only recipients a mail may actually reach. Everything else is
+# stripped from the envelope and a mail left without a recipient is not sent at all, see
+# App\EventListener\EmailRecipientWhitelistSubscriber. Empty means no filtering, which is what
+# production runs with. Set this on staging: it runs the real transports against real teamer
+# addresses. The patterns have to match the full address.
+# Example: APP_MAIL_RECIPIENT_WHITELIST='.*@ep-reisen\.de,qa@example\.com'
+APP_MAIL_RECIPIENT_WHITELIST=
+
 SFTP_XML_EXPORT_HOST=
 SFTP_XML_EXPORT_PORT=22
 SFTP_XML_EXPORT_USER=