Problem to send mail with mailtrap using Docker (MongoDB)

I'm studying the development of an API and I'm having trouble using mailtrap to do the test of sending email during user validation. The user is typed in the mongo however he does not send the email and returns the following error:

Error: connect ECONNREFUSED 127.0.0.1:587
at Object._errnoException (util.js:992:11)
at _exceptionWithHostPort (util.js:1014:20)
at TCPConnectWrap.afterConnect [as oncomplete] (net.js:1186:14)

I understood that this was a port error and went after the answers, I found a solution by creating a file called daemon.json inside the / etc / docker folder with the following DNS content:

    { "dns": ["89.101.160.5", "89.101.160.4"] }

The problem persisted in Ubuntu. I changed machine and mac with another Docker account, another container the error persists.

Does anyone know an exit?