feat: customer auth via email

lib/plugins/email/mailgun/mailgun.js

@@ -4,10 +4,11 @@ const NAME = 'Mailgun'
 
 function sendMessage ({apiKey, domain, fromEmail, toEmail}, rec) {
   const mailgun = Mailgun({apiKey, domain})
+  const to = req.email.toEmail ?? toEmail
 
   const emailData = {
     from: `Lamassu Server ${fromEmail}`,
-    to: toEmail,
+    to,
     subject: rec.email.subject,
     text: rec.email.body
   }