split mail and mailserver

mail = all the per-domain code
mailserver = all the mail server level code

src/reverseproxy.js

@@ -48,7 +48,7 @@ const acme2 = require('./acme2.js'),
     ejs = require('ejs'),
     eventlog = require('./eventlog.js'),
     fs = require('fs'),
-    mail = require('./mail.js'),
+    mailServer = require('./mailserver.js'),
     network = require('./network.js'),
     os = require('os'),
     path = require('path'),
@@ -173,7 +173,7 @@ function validateCertificate(subdomain, domain, certificate) {
 }
 
 async function notifyCertChange() {
-    await mail.checkCertificate();
+    await mailServer.checkCertificate();
     await shell.promises.sudo('notifyCertChange', [ RESTART_SERVICE_CMD, 'box' ], {}); // directory server
     const allApps = (await apps.list()).filter(app => app.runState !== apps.RSTATE_STOPPED);
     for (const app of allApps) {