By default, Mac Mail checks for new messages every 5 minutes, you can adjust this as follows:

1. Select Mail > Preferences
2. Click the General button
3. Click the Check for new mail drop-down menu, and then indicate how often Mac Mail should check for new messages. Note: We strongly recommend leaving this setting on the default 5 minute interval
4. Make changes to other mail settings as desired
5. Close the Accounts window
6. When prompted to save your changes, click the Save button