You may want to email just one applicant on a case-by-case basis. To email the applicant, first view the list of submissions and choose the submission.

You can easily email the applicant straight from viewing their submission by clicking the Email tab.
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You have the option to select a Template - the emails that appear here are configured in confirmation emails. One tip is to setup several confirmation emails and set them as disabled (do not send email) so that they are not sent out automatically when a submission is received, but that you can use them as templates like in the above example.