Add message/* mimetype file

tests/src/message.msg

@@ -0,0 +1,20 @@
+From: John Doe <example@example.com>
+MIME-Version: 1.0
+Content-Type: multipart/mixed;
+        boundary="XXXXboundary text"
+
+This is a multipart message in MIME format.
+
+--XXXXboundary text
+Content-Type: text/plain
+
+this is the body text
+
+--XXXXboundary text
+Content-Type: text/plain;
+Content-Disposition: attachment;
+        filename="test.txt"
+
+this is the attachment text
+
+--XXXXboundary text--