namespace Ardalis.GuardClauses { public static class InvalidEmailGuard { public static string InvalidEmail(this IGuardClause guardClause, string email, string parameterName) { Guard.Against.NullOrEmpty(email, nameof(email)); var emailSuffix = ".com"; if (!email.EndsWith(emailSuffix)) { throw new ArgumentException($"Invalid Email - must end in {emailSuffix}", parameterName); } return email; } } }