Assumes meteor collection-hooks is installed.

triggers.js

var my_coll = new Meteor.Collection('my_coll'),
  triggers = new Meteor.Collection('triggers'),
  TRIGGER_TYPES = [ greaterThanFive: 'greaterThanFive' ];

my_coll.after.update(function (userId, doc, fieldNames, modifier, options) {
  if (doc.count > 5) {
    _.each(triggers.find({ on: TRIGGER_TYPES.greaterThanFive }).fetch(), function (trig) {
      switch (trig.event) {
        case 'email':
          Email.send(trig.to, { html: trig.markup });
          break;
      }
    });
  }
});