I noticed there is an option: "Server email settings", what is this for?

It's designed for application of user account from an URL.

This is an automated email account for BigAnt server, so that the BigAnt system can send invitations to new users that you wish to added to BigAnt, you can find "invite users" from top-right pull down menu in BigAnt server console.

Launch your BigAnt console > System Diagnose > System Settings > E-mail Settings, enter your mail server, email address (which will be used to send notification emails to users and admin) and password.

Back to your BigAnt Admin console, click 'Edit profile' from the top right corner, and enter your email address to receive notification emails of account application.

In your BigAnt admin console, click 'Invite users' from the top right corner, share this link out to your users and let them to fill required info. (The required email address is used to receive notification of result) In addition, you need to build your OU structure in BigAnt console first, so that users can choose which department they are member of.

Admin can find the application record in your BigAnt console/Users/Account Approval, and agree or disagree with that application of user account. Also, the result will be sent to users via email.

Once the user account is approved, he/she can login to BigAnt from the client.