public static class ExceptionExtensions
{
    public static IEnumerable<Exception> FlatException(this Exception exception)
    {
        var innerException = exception;

        do
        {
            yield return innerException;
            innerException = innerException.InnerException;
        }
        while (innerException != null);
    }

    public static string FullExceptionMessage(this Exception exception)
    {
        var messages = exception.FlatException().Select(x => x.Message);
        var flatMessage = string.Join("\n", messages);

        return flatMessage;
    }
}