Yes, Interfolio provides many options and tools for sending notifications.
Administrative users can write messages to candidates when sending emails, when sharing files, and when clicking the "Notify Candidate" button.
See Also
Opus Support Site Articles
Can I Share Case Materials with a Review Candidate?
How Do I Have a Candidate Fill Out a Form?
How Does Candidate Certification Work in Interfolio?
Do I Have to Click the “Notify Candidate” Button?
Interfolio Help Center Articles
Notify a Candidate of Their Review