I've been asked to find out what companies are doing in regards to Ransomware and SharePoint. The question lies with e-mailing SharePoint Links that are hijacked along with the e-mail address and used as a Ransomware link that is sent back to an unsuspecting employee. How do you handle this?
To hijack SharePoint notifications you would have to do something like this: How can I create custom Alerts for external email addresses? you could periodically review the configuration files to make sure they have not been changed. (They are loaded in the DB, not on the server, so a standard file checker would not cut it.)
To Phish you would have to send from outside the network or spoof from inside the network. in both cases the email looks different. Mitigate with user education standard for phishing prevention ala security.stackexchange.com
To send malicious links from a SharePoint email however would be as trivial as adding a malicious link in a list and sending an alert to some users. This is neither ransomware nor SharePoint specific. Any system that sends an email could easily send bad links.
This should help you get started on risk assessment. I really hope this is not a buzzword evaluation style risk assessment. If you are trying to evaluate risk then take your time, select a framework, do the research, and then assess the risks using the framework. This seems like a VERY SPECIFIC question about risk of a particular product. I would rate this risk as possible (like all vulnerabilities) but with several hours of effort. Yet not very likely because of the effort involved to do this from SharePoint and the ease of doing the same thing from other routes.