The Web Tools application is an executable module, installed on the client computer. It exists to perform tasks that cannot be done from inside a Browser, such as downloading a file, starting an editor, and later uploading the same file.
From SuperOffice version 7.5 SR1 our web tools now use SignalR in stead of NPAPI. To help you diagnose problems easier on clients you may use the page found directly under your site called WebToolsDiagnostics.aspx, typically https://path.to.crm.web/WebToolsDiagnostics.aspx
If this shows a status 404 under status for hubLoaded
Verify that your website have ExtensionlessUrlHandler-Integrated-4.0 enabled under Handler Mappings in IIS for the web application.
If you have problems with MailLink, goo start to troubleshooting is this FAQ.