Creating Your Own Online E-mail System in ASP.NET 2.0

Since the amount of ground to be covered won't all fit in one article, the material will be covered in four parts. This first part will introduce the topic and dissect the key techniques.

Requirements and Goals

The online e-mail system to be introduced in this series of articles is actually a common online mailbox, with which you can send various kinds of e-mail, such as e-mail in text format, HTML format, and with attachments. Using the system in this series, you will also be able to manipulate your mailboxes and e-mail, such as by looking up the mailboxes and the e-mail in them.

Concretely, the main functions enabled by this system can be enumerated as follows:

• Sending common e-mails
• Sending HTML-formatted e-mails
• Sending e-mails with attachments
• Configuring the mail server
• Checking your mailboxes
• Checking the e-mails in your mailboxes
• Creating, renaming and deleting the folders
• Reading your e-mails
• Deleting your e-mails
• Moving your e-mails

Does this sound like a very useful and fun project? The next section will show you how to design the underlining part -- the database tier.

Database Design

With the general goals in mind, we can now focus upon the database design.

In this article, we'll design a database named WebMailDatabase.mdf, which contains four tables: Folders for holding mailbox folders, Mails for storing all the e-mails, Attachments for storing all the attachments of the related e-mails, and WebMailProfiles for holding information to configure your mail server. 

Now, for brevity, the table structures of the four tables are listed in table form respectively as follows:

Table 1-Structure for Folders Table

Table 2-Structure for Mails Table

Table 3-Structure for Attachments Table

Table 4-Structure for WebMailProfiles Table

Besides these four tables, we've also defined three stored procedures, namely Pr_DeleteMail, Pr_MoveMail and Pr_SaveAsMail used to delete the e-mails, move the e-mails and save the e-mails sent out, respectively. Here we don't list their relevant sql scripts, since there is still a long journey for us to make. For all detailed information, please refer to the downloadable source files accompanying this article.

Dissecting the Key Techniques: Interface Design

On the whole, there are two crucial parts in constructing the e-mail system: one is sending out the e-mails of different kinds, the other is profiling your mail server. To grasp the ideas in the two parts, you should acquaint yourself with the MAIL related API provided by the .NET 2.0 framework. Now let's look more closely at each part.

Sending E-mail

Here, we are merely interested in three kinds of mail (which in fact are the most commonly used), i.e. text format e-mails, HTML format e-mails, and those with attachments. Note that all these are done inside the Sender.aspx page.

1. Interface design

The following Figure 1 gives you the design time snapshot of the Sender.aspx page.

Figure 1-The design time snapshot of the Sender.aspx page

Since there is nothing peculiar here but the usual components for manipulating an e-mail, let's not chatter much about the controls but go on with the story.

Dissecting the Key Techniques: Sending Email

2. Sending emails

The whole process of sending email is rather complicated especially when the email contains attachments. Let's examine the detailed steps in terms of the three scenarios mentioned above, as follows:

1) Obtain the mail address of the sender, i.e. get the address the user has configured in the profile. The following gives the crucial code snippet associated with this:

string from =((WebMailProfile)HttpContext.Current.Application["WebMailProfile"]).Email;

MailMessage mailMsg = new MailMessage();

mailMsg.From = new MailAddress(from);

2) Add the addresses of the receivers. Since there may be more than one address receiving the e-mail, you need to get the address of every recipient from the string containing these addresses, and append them one by one to the To property of the MailMessage-mailMsg object:

string split = ";";

string[] toList = To.Text.Trim().Split(split.ToCharArray());

for(int i = 0; i < toList.Length; i++)

{

  mailMsg.To.Add(toList[i].Trim());

}

3) Add the CopyTo (i.e. CC) addresses. There may be more than one of this kind of address; your approach should be similar to the one taken above: 

string[] ccList = CC.Text.Trim().Split(split.ToCharArray());

for(int i = 0; i < ccList.Length; i++){

  if(ccList[i].Trim().Length > 0) {

    mailMsg.CC.Add(ccList[i].Trim());

}

}

4) Add the topic of the mail and give the appropriate coding algorithm:

mailMsg.Subject = Title.Text.Trim();

mailMsg.SubjectEncoding = Encoding.UTF8;

5) Append the body of the e-mail and also specify the coding methods:

mailMsg.Body = Body.Text;

mailMsg.BodyEncoding = Encoding.UTF8;

6) Specify the format of the email as HTML by default:

mailMsg.IsBodyHtml = HtmlCB.Checked;

7) Add the attachments. Here the reason and the operation are just like those of steps 2 or 3 above, so we simply list the relevant code below:

HttpFileCollection fileList = HttpContext.Current.Request.Files;

for(int i = 0; i < fileList.Count; i++)

{ ///adding each attachment

  HttpPostedFile file = fileList[i];

  if(file.FileName.Length <= 0 || file.ContentLength <= 0)

  {break;}

  Attachment attachment = new Attachment(file.FileName);

  mailMsg.Attachments.Add(attachment);

  nContain += file.ContentLength;

}

8) Start sending your e-mail. First, call the SendMail method of the Mail class (the wrapper of the mailing related operation for simplification). Second, use the SaveAsMail method of the Mail class to persist the e-mails sent into the Sender mailbox:

IMail mail = new Mail();

mail.SendMail(mailMsg);

///save the mails to send

int nMailID = mail.SaveAsMail(mailMsg.Subject,mailMsg.Body,from, To.Text.Trim(),CC.Text.Trim(),mailMsg.IsBodyHtml,

  nContain,mailMsg.Attachments.Count > 0 ? true : false);

9) If there are attachments for the e-mails, upload them to the hard disk of the server, and finally store information for these attachments in the database. This function is accomplished through the following:

for(int i = 0; i < fileList.Count; i++)

{ ///add each attachment

  HttpPostedFile file = fileList[i];

  if(file.FileName.Length <= 0 || file.ContentLength <= 0)

  {break;}

  /// store these attachments into the hard disk

  file.SaveAs(MapPath("MailAttachments/" + Path.GetFileName(file.FileName)));

  /// save the attachments

  mail.SaveAsMailAttachment(

    Path.GetFileName(file.FileName),

    "MailAttachments/" + Path.GetFileName(file.FileName),

    file.ContentType,

    file.ContentLength,

    nMailID);

}

Using SendMail

It's by using the SendMail method of the Mail class that you finally send out your e-mail. It first sets up the IP address and port for the mail server, then sets the mode of sending e-mails and whether to use user credentials, then finally it invokes the Send (MailMessage mailMsg) function to send the email.

public int SendMail(MailMessage mail)

{

  ///Define the client to sent the e-mail

  SmtpClient client = new SmtpClient();

  ///Set up the IP address of the mail server host

  client.Host = ((WebMailProfile)HttpContext.Current.Application["WebMailProfile"]).MailServerIP;

  ///set up the port of the mail server

  client.Port = ((WebMailProfile)HttpContext.Current.Application["WebMailProfile"]).MailServerPort;

  ///configure the properties for sending e-mails

  client.DeliveryMethod = SmtpDeliveryMethod.Network;

  //client.UseDefaultCredentials = false;

  client.UseDefaultCredentials = true;

  client.Credentials = new NetworkCredential("Xianzhong Zhu","abc123");

  //client.EnableSsl = true;

  ///send e-mail

  client.Send(mail);

  return (0);

}

Please check back next week for the continuation of this article.