Sends a QUIT message to the SMTP server, gracefully ends the TCP connection, and releases all resources used by the current instance of the SmtpClient class.
Assembly: System (in System.dll)
The connection established by the current instance of the SmtpClient class to the SMTP server may be re-used if an application wishes to send multiple messages to the same SMTP server. This is particularly useful when authentication or encryption are used establish a connection to the SMTP server. The process of authenticating and establishing a TLS session can be expensive operations. A requirement to re-establish a connection for each message when sending a large quantity of email to the same SMTP server could have a significant impact on performance. There are a number of high-volume email applications that send email status updates, newsletter distributions, or email alerts. Also many email client applications support an off-line mode where users can compose many email messages that are sent later when a connection to the SMTP server is established. It is typical for an email client to send all SMTP messages to a specific SMTP server (provided by the Internet service provider) that then forwards this email to other SMTP servers.
The SmtpClient class implementation pools SMTP connections so that it can avoid the overhead of re-establishing a connection for every message to the same server. An application may re-use the same SmtpClient object to send many different emails to the same SMTP server and to many different SMTP servers. As a result, there is no way to determine when an application is finished using the SmtpClient object and it should be cleaned up.
When an SMTP session is finished and the client wishes to terminate the connection, it must send a QUIT message to the server to indicate that it has no more messages to send. This allows the server to free up resources associated with the connection from the client and process the messages which were sent by the client.
The Dispose method iterates through all established connections to the SMTP server specified in the Host property and sends a QUIT message followed by gracefully ending the TCP connection. The Dispose method also releases the unmanaged resources used by the underlying Socket.
Call Dispose when you are finished using the SmtpClient. The Dispose method leaves the SmtpClient in an unusable state. After calling Dispose, you must release all references to the SmtpClient so the garbage collector can reclaim the memory that the SmtpClient was occupying.