diff --git a/internal/mail/message_test.go b/internal/mail/message_test.go
index 8919a3a4f..339fe2fb3 100644
--- a/internal/mail/message_test.go
+++ b/internal/mail/message_test.go
@@ -92,6 +92,13 @@ func Test_detectContentType(t *testing.T) {
 			},
 			"text/html; charset=\"UTF-8\"",
 		},
+		{
+			"plain-with-some-html",
+			args{
+				[]byte("Hi, this is plain text with example html included <h1>An example html tag</h1>"),
+			},
+			"text/plain; charset=\"UTF-8\"",
+		},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {