storage: Add Seen flag, tests for #58

pkg/message/message.go

@@ -21,6 +21,7 @@ type Metadata struct {
 	Date    time.Time
 	Subject string
 	Size    int64
+	Seen    bool
 }
 
 // Message holds both the metadata and content of a message.
@@ -109,3 +110,8 @@ func (d *Delivery) Size() int64 {
 func (d *Delivery) Source() (io.ReadCloser, error) {
 	return ioutil.NopCloser(d.Reader), nil
 }
+
+// Seen getter.
+func (d *Delivery) Seen() bool {
+	return d.Meta.Seen
+}