mailtuner.com => preference: 0
            server.mailtuner.com => preference: 10
            mail.mailtuner.com => preference: 11

host: 'server.mailtuner.com',
    port: 587,
    secure: false, // secure:true for port 465, secure:false for port 587
    auth: {
        user: 'postmaster@mailtuner.com',
        pass: 'XXXXX'
    }
});

{ Error: Hostname/IP doesn't match certificate's altnames: "Host: server.mailtuner.com. is not in the cert's altnames: DNS:mailtuner.com"
    at Object.checkServerIdentity (tls.js:222:17)
    at TLSSocket.<anonymous> (_tls_wrap.js:1110:29)
    at emitNone (events.js:105:13)
    at TLSSocket.emit (events.js:207:7)
    at TLSSocket._finishInit (_tls_wrap.js:638:8)
    at TLSWrap.ssl.onhandshakedone (_tls_wrap.js:468:38)
  reason: 'Host: server.mailtuner.com. is not in the cert's altnames: DNS:mailtuner.com',
  host: 'server.mailtuner.com',
  cert:
   { subject: { CN: 'mailtuner.com' },
     issuer:
      { C: 'US',
        O: 'Let's Encrypt',
        CN: 'Let's Encrypt Authority X3' },
     subjectaltname: 'DNS:mailtuner.com',
     infoAccess: { 'OCSP - URI': [Array], 'CA Issuers - URI': [Array] },
     modulus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
     exponent: '0x10001',
     valid_from: 'Nov  7 21:35:01 2017 GMT',
     valid_to: 'Feb  5 21:35:01 2018 GMT',
     fingerprint: '96:76:5D:D9:1C:D4:CD:50:75:60:D5:52:45:58:AB:5B:BD:D5:CB:F3',
     ext_key_usage: [ '1.3.6.1.5.5.7.3.1', '1.3.6.1.5.5.7.3.2' ],
     serialNumber: '0314E704EE42C2C26F7028950BAA826401A4',
     raw: <Buffer 30 82 04 fd 30 82 03 e5 a0 03 02 01 02 02 12 03 14 e7 04 ee 42 c2 c2 6f 70 28 95 0b aa 82 64 01 a4 30 0d 06 09 2a 86 48 86 f7 0d 01 01 0b 05 00 30 4a ... > },
  code: 'ESOCKET',
  command: 'CONN' }