.seek(0) on the message before passing stdin to the markup process

widgets/compose.go

@@ -541,6 +541,12 @@ func (c *Composer) GenerateMarkup(markupKey string) error {
 	}
 	go func() {
 		defer stdin.Close()
+        _, err := c.email.Seek(0, io.SeekStart)
+        if err != nil {
+            logging.Warnf("failed to seek beginning of mail: %v", err)
+            return
+        }
+
 		io.Copy(stdin, c.email)
 	}()
 	outBytes, err := proc.Output()