For large teams and groups operating under a single domain, it is sometimes easier to allow users to join the group by self-registering with their own email account. If you want users within your domain to register their email accounts by themselves the best option is to whitelist your domain. If the email domain (or set of domains) is whitelisted, each user that would register with an email from that domain will automatically join the Group.
Please contact support@explaineverything.com if you wish to use this option.