MailHog not Authenticating with GoMail

Question

We have a docker compose that connecting a golang mail service with a mailhog service. Below is the mailhog configuration in our docker-compose.yml:

mailhog:
      image: mailhog/mailhog:latest
      restart: always
      ports:
        - 1025:1025
        - 8025:8025
      networks:
         mercury:
            aliases:
               - mailhog.local

We are using gopkg.in/gomail.v2 package. Below is the function from the golang mail service within our docker-compose. This is the function that is returning the error:

func (e *Email) attemptToSendMessage(m structs.Message) {

    var s gomail.SendCloser
    var err error
    //If we want to disable any emails being sent, we have set an ENV var to disallow it.
    if !e.DisableEmail {
        d := gomail.NewDialer(e.smtpServer, e.smtpPort, e.smtpUser, e.smtpPassword)
        if s, err = d.Dial(); err != nil {
            log.WithFields(log.F("error", err)).Notice("Issue connecting to smtp server")
            e.failMessage(m)
            return
        }

        if err = gomail.Send(s, e.parseMessage(m)); err != nil {

            log.WithFields(log.F("error", err)).Notice("ERROR sending to smtp server, retrying")
            e.failMessage(m)
            s.Close()
            return
        }
        s.Close()
    }

When we attempt to connect though, we get the following error msg:

Dec 08 08:25:18 35.183.142.45 golang.mail.app.instance 2020-12-08T13:25:18.758599257Z NOTICE Issue connecting to smtp server error=unencrypted connection

Messsage returned from mailhog app.

Dec 08 08:25:18 35.183.142.45 mailhog.instance 2020/12/08 13:25:18 [SMTP 172.29.0.4:33526] Sent 16 bytes: '250 AUTH PLAIN\r\n'

Dec 08 08:25:18 35.183.142.45 mailhog.instance 2020/12/08 13:25:18 [SMTP 172.29.0.4:33526] Received 6 bytes: 'QUIT\r\n'