Once someone registers for your membership area or products the site can send them their login details. To do this you will need to get the SMTP details for your company support email (not recommended) or use the services of professional solutions such as Sendgrid.com
Third party services such as Sendgrid handle the load of emails and will ensure your emails get delivered. While you can do this with your own support email smtp details, this option is not recommended because of potential deliver-ability issues.
The service we recommend and we use ourselves is SendGrid