Email.java

package com.abc.model;

import java.util.List;

public class Email {

    private String from;
    private List<String> to;
    private List<String> cc;
    private List<String> bcc;
    private String subject;
    private String message;

    public Email() {}

    public Email(String from, List<String> to, List<String> cc, List<String> bcc) {
        this.from = from;
        this.to = to;
        this.cc = cc;
        this.bcc = bcc;
    }

    public Email(String from, List<String> to, List<String> cc, List<String> bcc, String subject, String message) {
        this.from = from;
        this.to = to;
        this.cc = cc;
        this.bcc = bcc;
        this.subject = subject;
        this.message = message;
    }

    public String getFrom() {
        return from;
    }

    public void setFrom(String from) {
        this.from = from;
    }

    public List<String> getTo() {
        return to;
    }

    public void setTo(List<String> to) {
        this.to = to;
    }

    public List<String> getCc() {
        return cc;
    }

    public void setCc(List<String> cc) {
        this.cc = cc;
    }

    public List<String> getBcc() {
        return bcc;
    }

    public void setBcc(List<String> bcc) {
        this.bcc = bcc;
    }

    public String getSubject() {
        return subject;
    }

    public void setSubject(String subject) {
        this.subject = subject;
    }

    public String getMessage() {
        return message;
    }

    public void setMessage(String message) {
        this.message = message;
    }
}

EmailServiceImpl.java

package com.abc;

import com.abc.model.Email;
import com.sun.jersey.api.client.Client;
import com.sun.jersey.api.client.ClientResponse;
import com.sun.jersey.api.client.WebResource;
import com.sun.jersey.api.client.filter.HTTPBasicAuthFilter;
import com.sun.jersey.core.util.MultivaluedMapImpl;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Service;

import javax.ws.rs.core.MediaType;

@Service
public class EmailServiceImpl implements EmailService {

    static final Logger logger = LoggerFactory.getLogger(EmailServiceImpl.class);

    @Value("${email.mailgun.apiKey}")
    private String mailgunApiKey;

    @Value("${email.mailgun.host}")
    private String mailgunHost;

    @Override
    public boolean send(Email email) {
        Client client = Client.create();
        client.addFilter(new HTTPBasicAuthFilter("api", mailgunApiKey));

        WebResource webResource = client.resource("https://api.mailgun.net/v2/" + mailgunHost +  "/messages");

        MultivaluedMapImpl formData = new MultivaluedMapImpl();
        formData.add("from", email.getFrom());
        formData.add("to", email.getTo().get(0));
        formData.add("subject", email.getSubject());
        formData.add("html", email.getMessage());

        ClientResponse clientResponse = webResource.type(MediaType.APPLICATION_FORM_URLENCODED).post(ClientResponse.class, formData);
        String output = clientResponse.getEntity(String.class);

        logger.info("Email sent successfully : " + output);
        return true;

    }
}