Corresponding directly with the candidate? You'll probably want to use Lever's email sync. Read on here.
Got a thread with a third-party that you'd like to sync onto a candidate's profile? For example, doing a backchannel reference and want to add the thread to the candidate? Use the Link email workflow:
1. Jump into the email thread in Gmail and open the Chrome extension. Search for the candidate who you'd like to add the thread onto:
2. Click to link this thread onto an existing candidate's profile:
3. You'll then see that the linking worked! Your email thread has been added onto the candidate's profile.