Small problem with ASP. NET Local Service field call (Webserice)

When there are global variables, such as: protected static dictionary<string, string> salesmail = new dictionary<string, string> ();

This variable is used every day when the program is run, such as adding data to the variable. If the service does not stop or restart, the variable will have the recorded data.

The problem I encountered is to send a reminder email with the expiry of the contract every morning, access the data every day, filter the data, and then place the mailbox in the Salesmail variable for the renewal of the email, and then send the message after the data filter ends. So the message that appeared yesterday or earlier, because the service did not stop, this variable has been a reference, and its data is not emptied. In our normal state, when the method calls this variable is the equivalent of re-instantiation of the variable, when the method executes this variable will be recycled. But the service is not so, it has been there, not recycled.

Small problem with ASP. NET Local Service field call (Webserice)