@Zack Heres one of my snippets that attaches to the contact and customer record. Both are internal id's of the records
// Send Email
email.send({
author: authorId,
recipients: contactId,
attachments: [pdfFileRedone],
relatedRecords: {
entityId: entityId,
entityId: contactId
},
subject: 'subject', //subjectFromTemplate,
body: 'body'//bodyFromTemplate
});