When someone joins a membership online, an email is sent from the backend. An example is shown below.

Hi Member,

We have received your registration details, thank you.
Your registration will be processed by our staff in the next few days.
Kind Regards,

Forrest Tennis Club
[email protected]

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This is an automated notification email. Please do not reply to this message. Replies will not be read or responded to.
Thank you.

To add copy email –

From Control Panel – Click Customer Properties.
Add  MEMBER_REGISTRATION_EMAIL_CC and the corresponding email id.