Sometimes when building websites, we need to generate email more than once. For example a site could have a contact form and a user-filled form, both generating email to the site owner. You don't need to be able to spout the name of every software pattern verbatim, to recognize the duplication here and the need to somehow factor it out.

We typically use the strategy pattern where we might have several different implementations of something and want to abstract out the common functionality. The strategy is also known as the provider pattern and I prefer this term. An interface is a good candidate data structure to use here because we can stipulate that a client class must implement a mailing method, and we can leave the details to that class. Let's look at some code...

Typical Scenario

Here are some typical Web.config email settings and code to send an email:

<appSettings>
    <add key="ToEmailAddr" value="info@mysite.com" />
    <add key="FromEmailAddr" value="info@mysite.com" />
</appSettings>

<system.net>
    <mailSettings>
        <smtp from="info@mysite.com">
            <network host="smtp.mymailserver.net" port="25" />
        </smtp>
    </mailSettings>
</system.net>

using System.Configuration;
using System.Net.Mail;
using System.Web.Configuration;

System.Configuration.Configuration config
  = WebConfigurationManager.OpenWebConfiguration(base.Request.ApplicationPath);
AppSettingsSection appSettings = (AppSettingsSection)config.GetSection("appSettings");

string toAddress = appSettings.Settings["ToEmailAddr"].Value;
string fromAddress = appSettings.Settings["FromEmailAddr"].Value;

SmtpClient smtpClient = new SmtpClient();

MailMessage message = new MailMessage();
message.IsBodyHtml = false
message.Priority = MailPriority.High;
message.DeliveryNotificationOptions = DeliveryNotificationOptions.OnFailure;

try
{
    message.Subject = "Subject: " + this.subjectBox.Text;
    message.Body = "Sender: " + nameBox.Text.Trim() + "\n";
    message.Body += "Street: " + streetBox.Text.Trim() + "\n";
    message.Body += "City: " + cityBox.Text.Trim() + "\n";
    message.Body += "State: " + stateDropDown.SelectedValue
        + " " + zipBox.Text.Trim() + "\n";
    message.Body += "Email: " + emailBox.Text.Trim() + "\n";
    message.Body += "\n\n" + this.messageBox.Text + "\n\n";

    smtpClient.Send(fromAddress, toAddress, message.Subject, message.Body);
}
catch (Exception ex)
{
    // Log error
}

Strategy Pattern

While this particular email example will not save us a whole lot of typing, it does enable us to implement the email functionality differently for each client class that uses it. This may be useful if we had to send mail through several different servers; in such a case we might also want to configure our settings in code, or factor out our Web.config sections. Factoring out parts of your Web.config is another topic and can be used to greatly simplify deployment.

interface IGenerateMail
{
    // Classes using this interface must implement this method
    void SendMail(string to, string from, string subject, string body);
}

// Implementing the Strategy Pattern
public class RealtySMTPMailer : IGenerateMail
{
    //(string from, string to, string subject, string message)
    public void SendMail(string from, string to, string subject, string message)
    {
        MailMessage realtyMessage = new MailMessage(from, to, subject, message);
        SmtpClient smtpClient = new SmtpClient();

        realtyMessage.IsBodyHtml = false;
        realtyMessage.Priority = MailPriority.High;
        realtyMessage.DeliveryNotificationOptions = DeliveryNotificationOptions.OnFailure;

        smtpClient.Send(from, to, subject, message);
    }
}

// Snippets from revised contact form
...
private RealtySMTPMailer mailProvider;

public Contact()
{
    mailProvider = new RealtySMTPMailer();
}

public Contact(RealtySMTPMailer mailProvider)
{
    this.mailProvider = mailProvider;
}
...

// Send button event handler
System.Configuration.Configuration config
  = WebConfigurationManager.OpenWebConfiguration(base.Request.ApplicationPath);
AppSettingsSection appSettings = (AppSettingsSection)config.GetSection("appSettings");

string toAddress = appSettings.Settings["ToEmailAddr"].Value;
string fromAddress = appSettings.Settings["FromEmailAddr"].Value;

StringBuilder mailBody = new StringBuilder();

mailBody.Append("From:" + " " + nameBox.Text.Trim() + "\n");
mailBody.Append("Address:" + " "
    + streetBox.Text.Trim() + ", "
    + cityBox.Text.Trim() + ", "
    + stateDropDown.SelectedValue + " "
    + zipBox.Text.Trim() + "." + "\n");
mailBody.Append("Email:" + " " + fromAddress + "\n\n");    
mailBody.Append("Message:" + "\n" + messageBox.Text.Trim());

mailProvider.SendMail(fromAddress, toAddress, subjectBox.Text.Trim(), mailBody.ToString());

We can now implement email functionality anywhere in the site and change that implementation without breaking code elsewhere. You might notice some refactoring going on in the last snippet; I substituted a string builder to construct the email, as it is more efficient. Remember, when refactoring you must resist the temptation to re-code the logic.

ASP.NET Email Resources

Sending Email with System.Net.Mail - Scott Guthrie

Sending Email in a Development Environment without an SMTP Server

Sending Email from ASP.NET using your Gmail Account