Let’s day I have a service that sends emails. This class also needs DI to get settings and add a logger. Here’s a trivial implementation:

public interface IEmailService
{
     public string From { get; set; }
     public string To { get; set; }
     public string Cc { get; set; }
     public string Subject { get; set; }
     public string Body { get; set; }
     
     public bool Send();
}

public class EmailService: IEmailService
{
     private readonly IOptions<EMailSettings> _settings;
     private readonly IEmailLogService _logService;

     public string From { get; set; }
     public string To { get; set; }
     public string Cc { get; set; }
     public string Subject { get; set; }
     public string Body { get; set; }
     
     public EmailService(IOptions<EMailSettings> settings, IEmailLogService logService)
     {
          _settings = settings;
          _logService = logService;
     }

     public bool Send()
     {
          SmtpClient smtpClient = new SmtpClient(_settings.SmtpHost);
          MailMessage message= new System.Net.Mail.MailMessage(new MailAddress(From), new MailAddress(To));
          message.Subject = Subject;
          message.Body = Body;
          if (Cc != null)
               message.CC.Add(Cc);

          smtpClient.Send(message);

          logService.log();

          return true;
     }
}

Now I have another service that needs to send emails

public interface ISomeService
{
     public void SendEmails();
}

public class SomeService: ISomeService
{
     private readonly IEmailService _emailService;

     public SomeService(IEmailService emailService)
     {
          _emailService = emailService;
     }

     public void SendEmails()
     {
          // Send first email
          _emailService.From = "[email protected]";
          _emailService.To = "[email protected]";
          _emailService.Cc= "[email protected]";
          _emailService.Subject = "My Subject";
          _emailService.Body= "My Message";
          _emailService.Send();

          // Send 2nd email
          _emailService.From = "[email protected]";
          _emailService.To = "[email protected]";
          _emailService.Subject = "My Subject 2";
          _emailService.Body= "My Message 2";
          _emailService.Send();
     }
}

You can see that _emailService is a shared member and my 2nd email inadvertently has a Cc set from the previous message. Other than having to blank out fields how can I create multiple EmailService objects that don’t share data?