Meteor mailgun send email exception

I get this error when try to register a new user in my meteor application:

I20160920-12:33:04.250(1)? Exception while invoking method 'createUser' Error: connect ECONNREFUSED 104.130.177.23:587 I20160920-12:33:04.251(1)? at Object.Future.wait (/Users/hakanmehmed/.meteor/packages/meteor-tool/.1.4.1_1.1ft26we++os.osx.x86_64+web.browser+web.cordova/mt-os.osx.x86_64/dev_bundle/server-lib/node_modules/fibers/future.js:449:15) I20160920-12:33:04.251(1)? at smtpSend (packages/email/email.js:89:1) I20160920-12:33:04.252(1)? at Object.Email.send (packages/email/email.js:192:1) I20160920-12:33:04.252(1)? at AccountsServer.Accounts.sendVerificationEmail (packages/accounts-password/password_server.js:802:9) I20160920-12:33:04.253(1)? at packages/accounts-password/password_server.js:1044:18 I20160920-12:33:04.253(1)? at tryLoginMethod (packages/accounts-base/accounts_server.js:248:14) I20160920-12:33:04.253(1)? at AccountsServer.Ap._loginMethod (packages/accounts-base/accounts_server.js:381:5) I20160920-12:33:04.253(1)? at [object Object].createUser (packages/accounts-password/password_server.js:1020:19) I20160920-12:33:04.253(1)? at maybeAuditArgumentChecks (packages/ddp-server/livedata_server.js:1711:12) I20160920-12:33:04.254(1)? at packages/ddp-server/livedata_server.js:711:19 I20160920-12:33:04.254(1)? - - - - - I20160920-12:33:04.254(1)? at Object.exports._errnoException (util.js:907:11) I20160920-12:33:04.254(1)? at exports._exceptionWithHostPort (util.js:930:20) I20160920-12:33:04.254(1)? at TCPConnectWrap.afterConnect [as oncomplete] (net.js:1077:14)

It appeared after I added the code to send verification emails to new users.

import { Meteor } from 'meteor/meteor';

Meteor.startup(() => {
  process.env.MAIL_URL = 'http://smtppostmaster%40[sandbox].mailgun.org:[passoword]@smtp.mailgun.org:587';
  Accounts.config({
    sendVerificationEmail: true
    });
});

I am using the accounts-ui package so I do not invoke createUser() myself.