diff --git a/internal/common/common.go b/internal/common/common.go
index a2a8d5c..8e26421 100644
--- a/internal/common/common.go
+++ b/internal/common/common.go
@@ -7,8 +7,10 @@ const (
 )
 
 const (
-	MIMETextHTML            string = "text/html"
-	MIMETextHTMLCharsetUTF8 string = MIMETextHTML + "; " + charsetUTF8
+	MIMETextHTML             string = "text/html"
+	MIMETextHTMLCharsetUTF8  string = MIMETextHTML + "; " + charsetUTF8
+	MIMETextPlain            string = "text/plain"
+	MIMETextPlainCharsetUTF8 string = MIMETextPlain + "; " + charsetUTF8
 )
 
 const Und string = "und"