By only allowing inviting users of specific email domains, eg your company domain, you can "prevent" to some extend that third party people may be added.

• This way it can prevent that for example admins give access to third party agencies without a super user's knowledge. Preventing data sharing.
• This way it can prevent some cases where a security issue could allow someone changing the email or inviting an email or adding a user with a third party email.

There should be a security setting where optionally a sysadmin can restrict the domains to one or multiple domains.

If any are defined, and then a user tries to invite|add|change a user email from a different domain, then an error would be shown that this is not allowed and to contact a super user.

To be defined:

• When adding or removing domains in the system setting but users with other domains exist. I suggest for simplicity we would show an error that this setting cannot be changed until all users match that criteria. Meaning a super user would need to first remove certain users and then change the setting again or allow additional domains.