In the Membership Management area, click on the settings button.

This takes you to a screen where you can choose which officers will receive emails when guests or members opt in, don't opt in, or are deleted.

To choose more than one officer, hold down the Ctrl key (Windows or Linux) or the Cmd key (Mac) while you make your choices.

If you want the new member to receive the new member welcome email as soon as they opt in, check the box (circled). Otherwise, the email will need to be sent manually.