diff --git a/mail.go b/mail.go
index <HASH>..<HASH> 100644
--- a/mail.go
+++ b/mail.go
@@ -54,12 +54,19 @@ func IsMultipartMessage(mailMsg *mail.Message) bool {
 // Valid Attachment-Headers:
 //
 //    Content-Disposition: attachment; filename="frog.jpg"
+//    Content-Type: attachment; filename="frog.jpg"
 //
 func IsAttachment(header mail.Header) bool {
 	mediatype, _, _ := mime.ParseMediaType(header.Get("Content-Disposition"))
 	if strings.ToLower(mediatype) == "attachment" {
 		return true
 	}
+
+	mediatype, _, _ = mime.ParseMediaType(header.Get("Content-Type"))
+	if strings.ToLower(mediatype) == "attachment" {
+		return true
+	}
+
 	return false
 }
 
diff --git a/mail_test.go b/mail_test.go
index <HASH>..<HASH> 100644
--- a/mail_test.go
+++ b/mail_test.go
@@ -264,6 +264,10 @@ func TestIsAttachment(t *testing.T) {
 			},
 		},
 		{
+			result: true,
+			header: mail.Header{"Content-Type": []string{"attachment; filename=\"test.jpg\""}},
+		},
+		{
 			result: false,
 			header: mail.Header{"Content-Disposition": []string{"non-attachment; filename=\"frog.jpg\""}},
 		},
Missing check for Content-Type header.

The check for Content-Type header in IsAttachment was missing.