Add NotificationSender, one test

atst/models/__init__.py

@@ -17,5 +17,6 @@ from .portfolio_invitation import PortfolioInvitation
 from .application_invitation import ApplicationInvitation
 from .task_order import TaskOrder
 from .dd_254 import DD254
+from .notification_recipient import NotificationRecipient
 
 from .mixins.invites import Status as InvitationStatus

atst/models/notification_recipient.py

@@ -0,0 +1,10 @@
+from sqlalchemy import String, Column
+
+from atst.models import Base, types, mixins
+
+
+class NotificationRecipient(Base, mixins.TimestampsMixin):
+    __tablename__ = "notification_recipients"
+
+    id = types.Id()
+    email = Column(String, nullable=False)