Admin panel:

Only invited user can register in strict mode,
Set mail server in admin panel,
Switch strict mode in admin panel,
Invite people to system in admin panel

models/invitationCodes.js

@@ -0,0 +1,45 @@
+InvitationCodes = new Mongo.Collection('invitation_codes');
+
+InvitationCodes.attachSchema(new SimpleSchema({
+  code: {
+    type: String,
+  },
+  email: {
+    type: String,
+    unique: true,
+    regEx: SimpleSchema.RegEx.Email,
+  },
+  createdAt: {
+    type: Date,
+    denyUpdate: false,
+  },
+  // always be the admin if only one admin
+  authorId: {
+    type: String,
+  },
+  boardsToBeInvited: {
+    type: [String],
+    optional: true,
+  },
+  valid: {
+    type: Boolean,
+    defaultValue: true,
+  },
+}));
+
+InvitationCodes.helpers({
+  author(){
+    return Users.findOne(this.authorId);
+  },
+});
+
+// InvitationCodes.before.insert((userId, doc) => {
+  // doc.createdAt = new Date();
+  // doc.authorId = userId;
+// });
+
+if (Meteor.isServer) {
+  Boards.deny({
+    fetch: ['members'],
+  });
+}