qr code generator asp net c# Mail in Visual C#

Creation QR Code in Visual C# Mail

15

Often, sending an e-mail message is simple and requires only two lines of code. However, as with any network communication, it can become much more complex. If the server is unresponsive, you need to allow users to decide whether to wait for or cancel the message transfer. Some servers require valid user credentials, so you might need to provide a username and password. When possible, you should enable the Secure Sockets Layer (SSL) to encrypt the message in transit and reduce your security risks.

After this lesson, you will be able to:

Configure an SMTP server, and send an e-mail message. Provide a username and password when required to authenticate to an SMTP server. Enable SSL to encrypt SMTP communications. Send a message asynchronously to allow your application to respond to the user or perform other tasks while an e-mail is being sent. Catch and respond to different exceptions that might be thrown while sending a message.

Once you create a message, you need to send it through an SMTP (Simple Message Transfer Protocol) server, which in turn will forward it to the recipient. In the .NET Framework, the SmtpClient class represents the SMTP server. Most of the time, sending a message is as simple as this sample code (where smtp.contoso.com is the name of the local SMTP server):

' VB Dim m As MailMessage = New MailMessage _ ("jane@contoso.com", _ "ben@contoso.com", _ "Quarterly data report.", _ "See the attached spreadsheet.") Dim client As SmtpClient = New SmtpClient("smtp.contoso.com") client.Send(m) // C# MailMessage m = new MailMessage ("jane@northrup.org", "ben@northrup.org", "Quarterly data report.",

"See the attached spreadsheet."); SmtpClient client = new SmtpClient("smtp.contoso.com"); client.Send(m);

The SmtpClient.PickupDirectoryLocation property is intended for Web applications. To send messages through an IIS-based SMTP server, specify the host name of the IIS server just like you would any other SMTP server. To specify the local computer, use localhost or 127.0.0.1 .

Tony Northrup Years ago, I used to recommend that everyone install IIS, enable the SMTP service on the computer that would be running their application, and send messages through the local SMTP server. This process is much more efficient than using a remote SMTP server because the local IIS SMTP server will directly contact each recipient s SMTP servers to send the message. Additionally, you don t have to deal with network connections. However, this approach became unreliable as organizations battled against spam. Organizations now block incoming messages from large blocks of IP addresses. Even if you are not a spammer, messages sent from a local SMTP server might be rejected if your IP address appears on one of these lists. To make it more complicated, you might be able to send messages to most domains but be rejected by others. Ultimately, the job of managing SMTP servers is now too complex to have every user running their own mail server. As a result, I now recommend people use their ISP s or their organization s mail server for outgoing messages.

Many things can go wrong when sending e-mail. For example, the mail server might not be available, the server might reject your user credentials, or the server might determine that one of your recipients is invalid. In each of these circumstances, the runtime will throw an exception, and your application must be prepared to catch the exception.

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When you send a message, you should always be prepared to catch an SmtpException. Messages are frequently rejected because the SMTP server cannot be found, the server identified the message as spam, or the server requires a username and password. You should also catch SmtpFailedRecipientException, which the runtime will throw if the SMTP server rejects a recipient e-mail address. SMTP servers reject only local recipients. In other words, if you are sending a message to tony@contoso.com and are using Contoso s SMTP server, the server is likely to reject the message if tony@contoso.com is not a valid address (causing the runtime to throw a SmtpFailedRecipientException). However, if you are sending a message to the same invalid address using Fabrikam s SMTP server, the SMTP server will not be able to identify that the e-mail address is invalid. Therefore, the runtime will not throw an exception. Table 15-1 summarizes these and other exceptions that the runtime might throw.

Table 15-1