TF-825 Download email as EML file (#2854)

model/lib/email/eml_attachment.dart

@@ -0,0 +1,15 @@
+
+import 'package:model/email/attachment.dart';
+
+class EMLAttachment extends Attachment {
+
+  EMLAttachment({
+    super.partId,
+    super.blobId,
+    super.size,
+    super.name,
+    super.type,
+    super.cid,
+    super.disposition,
+  });
+}