I sent an email containing a link to a SharePoint document, but the link is not accessible to the recipients.
SharePoint document links are available to your recipients only if they have access to the SharePoint server, and have sufficient permissions to view the document. Otherwise, they receive an error message when clicking the link, with an option to Request access to the document.
SharePoint provides a mechanism to request access to a site. If your recipients do not have sufficient permissions, they should follow the Request access link (SharePoint 2010) or click the Send Request button (SharePoint 2013 and later), to request permissions to the attached document, from the site owner.