You can set the auto response rule in sales force for web to lead and case auto response rules.
To create a Auto response rule:-
Setup, enter Auto-Response Rules in the Quick Find box, then select Lead Auto-Response Rules.
On the Auto-Response Rules page:
Click on the New Button.
Enter the rule name.
Check the active box to make this rule active.
Click Save.
Define the rule entries based on the conditions.
To create a response rule for cases:-
Setup, enter Auto-Response Rules in the Quick Find box, then select Case Auto-Response Rules.