Gets or sets a value that specifies the amount of time after which a synchronous Send call times out.
Assembly: System (in System.dll)
By default, calls to the Send method block until the operation completes. If you set the property to a positive value, and a Send operation cannot complete in the allotted time, the SmtpClient class throws an SmtpException exception.
To send a message and continue executing in the application thread, use the SendAsync method.