All pages in School Loop generate links, these links are referred to as System-generated links. These links can be copied and shared with any intended audience by granting due permissions.
Refer to this article to learn more about document sharing and granting permissions to shared documents.
The system-generated links on School Loop are sharable. However, in no case does having that link, give people the access to those system generated pages, like LoopMail.
Let us consider the example of LoopMail, even if the user has login credentials and access rights to LoopMail, they cannot load the message itself in order to reply via a shared link. School Loop provides the facility wherein Loopmail can actually be set up to notify the user's personal email as well if there is a new Loopmail message. So, whenever there is a new mail, a notification is sent to the user's registered personal email ID, however, the user can only open the message and read its contents.
The user cannot reply to the message from the personal email or open his Loopmail account using the link sent to his personal email. When you click on the Reply or Reply All links in the email, the user is redirected to login to School Loop. A message is displayed saying "Login Required" and the user's login name is pre-populated.
The user has to login to his School Loop account in order to access his Loopmail Inbox and then reply to the mail.