You have three options: 

1. Go to Candidates, click the three dots by a chosen candidate and select Send message.

NOTE: to use this option, you first need to integrate your mailbox with Traffit.

2. Open a candidate profile, hover over the red circle at the bottom right of the screen, and choose: Send mail to applicant. 

3. From the list of candidates in a job - to a particular candidate or to a multiple candidates at a time: