Envía correos electrónicos

Existen dos maneras de enviar correos electrónicos con la API de Gmail:

  • Puedes enviarlo directamente con el método messages.send.
  • Puedes enviarlo desde un borrador con el método drafts.send.

Los correos electrónicos se envían como strings codificadas en base64url dentro de la propiedad raw de un recurso de mensaje. El flujo de trabajo de alto nivel para enviar un correo electrónico es el siguiente:

  1. Crea el contenido del correo electrónico de una manera conveniente y codifícalo como una string base64url.
  2. Crea un recurso de mensaje nuevo y establece su propiedad raw en la string base64url que acabas de crear.
  3. Llama a messages.send o, si envías un borrador, a drafts.send para enviar el mensaje.

Los detalles de este flujo de trabajo pueden variar según la biblioteca cliente y el lenguaje de programación que elijas.

Creación de mensajes

La API de Gmail requiere mensajes de correo electrónico MIME que cumplan con RFC 2822 y estén codificados como strings base64url. Muchos lenguajes de programación tienen bibliotecas o utilidades que simplifican el proceso de creación y codificación de mensajes MIME. En los siguientes ejemplos de código, se muestra cómo crear un mensaje MIME con las bibliotecas cliente de las APIs de Google para varios lenguajes.

Java

La creación de un mensaje de correo electrónico se puede simplificar mucho con la clase MimeMessage en el paquete javax.mail.internet. En el siguiente ejemplo, se muestra cómo crear el mensaje de correo electrónico, incluidos los encabezados:

gmail/snippets/src/main/java/CreateEmail.java
import java.util.Properties;
import javax.mail.MessagingException;
import javax.mail.Session;
import javax.mail.internet.InternetAddress;
import javax.mail.internet.MimeMessage;

/* Class to demonstrate the use of Gmail Create Email API  */
public class CreateEmail {

  /**
   * Create a MimeMessage using the parameters provided.
   *
   * @param toEmailAddress   email address of the receiver
   * @param fromEmailAddress email address of the sender, the mailbox account
   * @param subject          subject of the email
   * @param bodyText         body text of the email
   * @return the MimeMessage to be used to send email
   * @throws MessagingException - if a wrongly formatted address is encountered.
   */
  public static MimeMessage createEmail(String toEmailAddress,
                                        String fromEmailAddress,
                                        String subject,
                                        String bodyText)
      throws MessagingException {
    Properties props = new Properties();
    Session session = Session.getDefaultInstance(props, null);

    MimeMessage email = new MimeMessage(session);

    email.setFrom(new InternetAddress(fromEmailAddress));
    email.addRecipient(javax.mail.Message.RecipientType.TO,
        new InternetAddress(toEmailAddress));
    email.setSubject(subject);
    email.setText(bodyText);
    return email;
  }
}

El siguiente paso es codificar el MimeMessage, crear una instancia de un objeto Message y establecer la string del mensaje codificada en base64url como el valor de la propiedad raw.

gmail/snippets/src/main/java/CreateMessage.java
import com.google.api.services.gmail.model.Message;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import javax.mail.MessagingException;
import javax.mail.internet.MimeMessage;
import org.apache.commons.codec.binary.Base64;

/* Class to demonstrate the use of Gmail Create Message API */
public class CreateMessage {

  /**
   * Create a message from an email.
   *
   * @param emailContent Email to be set to raw of message
   * @return a message containing a base64url encoded email
   * @throws IOException        - if service account credentials file not found.
   * @throws MessagingException - if a wrongly formatted address is encountered.
   */
  public static Message createMessageWithEmail(MimeMessage emailContent)
      throws MessagingException, IOException {
    ByteArrayOutputStream buffer = new ByteArrayOutputStream();
    emailContent.writeTo(buffer);
    byte[] bytes = buffer.toByteArray();
    String encodedEmail = Base64.encodeBase64URLSafeString(bytes);
    Message message = new Message();
    message.setRaw(encodedEmail);
    return message;
  }
}

Python

En la siguiente muestra de código, se explica cómo crear un mensaje MIME, codificar a una string base64url y asignarlo al campo raw del recurso Message:

gmail/snippet/enviar correo/create_draft.py
from __future__ import print_function

import base64
from email.message import EmailMessage

import google.auth
from googleapiclient.discovery import build
from googleapiclient.errors import HttpError


def gmail_create_draft():
    """Create and insert a draft email.
       Print the returned draft's message and id.
       Returns: Draft object, including draft id and message meta data.

      Load pre-authorized user credentials from the environment.
      TODO(developer) - See https://developers.google.com/identity
      for guides on implementing OAuth2 for the application.
    """
    creds, _ = google.auth.default()

    try:
        # create gmail api client
        service = build('gmail', 'v1', credentials=creds)

        message = EmailMessage()

        message.set_content('This is automated draft mail')

        message['To'] = 'gduser1@workspacesamples.dev'
        message['From'] = 'gduser2@workspacesamples.dev'
        message['Subject'] = 'Automated draft'

        # encoded message
        encoded_message = base64.urlsafe_b64encode(message.as_bytes()).decode()

        create_message = {
            'message': {
                'raw': encoded_message
            }
        }
        # pylint: disable=E1101
        draft = service.users().drafts().create(userId="me",
                                                body=create_message).execute()

        print(F'Draft id: {draft["id"]}\nDraft message: {draft["message"]}')

    except HttpError as error:
        print(F'An error occurred: {error}')
        draft = None

    return draft


if __name__ == '__main__':
    gmail_create_draft()

Creación de mensajes con archivos adjuntos

Crear un mensaje con un archivo adjunto es como crear cualquier otro mensaje, pero el proceso de subir el archivo como un mensaje MIME de varias partes depende del lenguaje de programación. En los siguientes ejemplos de código, se muestran formas posibles de crear un mensaje MIME de varias partes con un archivo adjunto.

Java

En el siguiente ejemplo, se muestra cómo crear un mensaje MIME de varias partes. Los pasos de codificación y asignación son los mismos que los anteriores.

gmail/snippets/src/main/java/CreateDraftWithAttachment.java
import com.google.api.client.googleapis.json.GoogleJsonError;
import com.google.api.client.googleapis.json.GoogleJsonResponseException;
import com.google.api.client.http.HttpRequestInitializer;
import com.google.api.client.http.javanet.NetHttpTransport;
import com.google.api.client.json.gson.GsonFactory;
import com.google.api.services.gmail.Gmail;
import com.google.api.services.gmail.GmailScopes;
import com.google.api.services.gmail.model.Draft;
import com.google.api.services.gmail.model.Message;
import com.google.auth.http.HttpCredentialsAdapter;
import com.google.auth.oauth2.GoogleCredentials;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.IOException;
import java.util.Properties;
import javax.activation.DataHandler;
import javax.activation.DataSource;
import javax.activation.FileDataSource;
import javax.mail.MessagingException;
import javax.mail.Multipart;
import javax.mail.Session;
import javax.mail.internet.InternetAddress;
import javax.mail.internet.MimeBodyPart;
import javax.mail.internet.MimeMessage;
import javax.mail.internet.MimeMultipart;
import org.apache.commons.codec.binary.Base64;

/* Class to demonstrate the use of Gmail Create Draft with attachment API */
public class CreateDraftWithAttachment {
  /**
   * Create a draft email with attachment.
   *
   * @param fromEmailAddress - Email address to appear in the from: header.
   * @param toEmailAddress   - Email address of the recipient.
   * @param file             - Path to the file to be attached.
   * @return the created draft, {@code null} otherwise.
   * @throws MessagingException - if a wrongly formatted address is encountered.
   * @throws IOException        - if service account credentials file not found.
   */
  public static Draft createDraftMessageWithAttachment(String fromEmailAddress,
                                                       String toEmailAddress,
                                                       File file)
      throws MessagingException, IOException {
        /* Load pre-authorized user credentials from the environment.
         TODO(developer) - See https://developers.google.com/identity for
          guides on implementing OAuth2 for your application.*/
    GoogleCredentials credentials = GoogleCredentials.getApplicationDefault()
        .createScoped(GmailScopes.GMAIL_COMPOSE);
    HttpRequestInitializer requestInitializer = new HttpCredentialsAdapter(credentials);

    // Create the gmail API client
    Gmail service = new Gmail.Builder(new NetHttpTransport(),
        GsonFactory.getDefaultInstance(),
        requestInitializer)
        .setApplicationName("Gmail samples")
        .build();

    // Create the email content
    String messageSubject = "Test message";
    String bodyText = "lorem ipsum.";

    // Encode as MIME message
    Properties props = new Properties();
    Session session = Session.getDefaultInstance(props, null);
    MimeMessage email = new MimeMessage(session);
    email.setFrom(new InternetAddress(fromEmailAddress));
    email.addRecipient(javax.mail.Message.RecipientType.TO,
        new InternetAddress(toEmailAddress));
    email.setSubject(messageSubject);

    MimeBodyPart mimeBodyPart = new MimeBodyPart();
    mimeBodyPart.setContent(bodyText, "text/plain");
    Multipart multipart = new MimeMultipart();
    multipart.addBodyPart(mimeBodyPart);
    mimeBodyPart = new MimeBodyPart();
    DataSource source = new FileDataSource(file);
    mimeBodyPart.setDataHandler(new DataHandler(source));
    mimeBodyPart.setFileName(file.getName());
    multipart.addBodyPart(mimeBodyPart);
    email.setContent(multipart);

    // Encode and wrap the MIME message into a gmail message
    ByteArrayOutputStream buffer = new ByteArrayOutputStream();
    email.writeTo(buffer);
    byte[] rawMessageBytes = buffer.toByteArray();
    String encodedEmail = Base64.encodeBase64URLSafeString(rawMessageBytes);
    Message message = new Message();
    message.setRaw(encodedEmail);

    try {
      // Create the draft message
      Draft draft = new Draft();
      draft.setMessage(message);
      draft = service.users().drafts().create("me", draft).execute();
      System.out.println("Draft id: " + draft.getId());
      System.out.println(draft.toPrettyString());
      return draft;
    } catch (GoogleJsonResponseException e) {
      // TODO(developer) - handle error appropriately
      GoogleJsonError error = e.getDetails();
      if (error.getCode() == 403) {
        System.err.println("Unable to create draft: " + e.getDetails());
      } else {
        throw e;
      }
    }
    return null;
  }
}

Python

Al igual que en el ejemplo anterior, en este ejemplo también se controla la codificación del mensaje en base64url y se la asigna al campo raw del recurso Message.

gmail/snippet/enviar correo/create_draft_with_attachment.py
from __future__ import print_function

import base64
import mimetypes
import os
from email.message import EmailMessage
from email.mime.audio import MIMEAudio
from email.mime.base import MIMEBase
from email.mime.image import MIMEImage
from email.mime.text import MIMEText

import google.auth
from googleapiclient.discovery import build
from googleapiclient.errors import HttpError


def gmail_create_draft_with_attachment():
    """Create and insert a draft email with attachment.
       Print the returned draft's message and id.
      Returns: Draft object, including draft id and message meta data.

      Load pre-authorized user credentials from the environment.
      TODO(developer) - See https://developers.google.com/identity
      for guides on implementing OAuth2 for the application.
    """
    creds, _ = google.auth.default()

    try:
        # create gmail api client
        service = build('gmail', 'v1', credentials=creds)
        mime_message = EmailMessage()

        # headers
        mime_message['To'] = 'gduser1@workspacesamples.dev'
        mime_message['From'] = 'gduser2@workspacesamples.dev'
        mime_message['Subject'] = 'sample with attachment'

        # text
        mime_message.set_content(
            'Hi, this is automated mail with attachment.'
            'Please do not reply.'
        )

        # attachment
        attachment_filename = 'photo.jpg'
        # guessing the MIME type
        type_subtype, _ = mimetypes.guess_type(attachment_filename)
        maintype, subtype = type_subtype.split('/')

        with open(attachment_filename, 'rb') as fp:
            attachment_data = fp.read()
        mime_message.add_attachment(attachment_data, maintype, subtype)

        encoded_message = base64.urlsafe_b64encode(mime_message.as_bytes()).decode()

        create_draft_request_body = {
            'message': {
                'raw': encoded_message
            }
        }
        # pylint: disable=E1101
        draft = service.users().drafts().create(userId="me",
                                                body=create_draft_request_body)\
            .execute()
        print(F'Draft id: {draft["id"]}\nDraft message: {draft["message"]}')
    except HttpError as error:
        print(F'An error occurred: {error}')
        draft = None
    return draft


def build_file_part(file):
    """Creates a MIME part for a file.

    Args:
      file: The path to the file to be attached.

    Returns:
      A MIME part that can be attached to a message.
    """
    content_type, encoding = mimetypes.guess_type(file)

    if content_type is None or encoding is not None:
        content_type = 'application/octet-stream'
    main_type, sub_type = content_type.split('/', 1)
    if main_type == 'text':
        with open(file, 'rb'):
            msg = MIMEText('r', _subtype=sub_type)
    elif main_type == 'image':
        with open(file, 'rb'):
            msg = MIMEImage('r', _subtype=sub_type)
    elif main_type == 'audio':
        with open(file, 'rb'):
            msg = MIMEAudio('r', _subtype=sub_type)
    else:
        with open(file, 'rb'):
            msg = MIMEBase(main_type, sub_type)
            msg.set_payload(file.read())
    filename = os.path.basename(file)
    msg.add_header('Content-Disposition', 'attachment', filename=filename)
    return msg


if __name__ == '__main__':
    gmail_create_draft_with_attachment()

Cómo mandar mensajes

Una vez que hayas creado un mensaje, puedes enviarlo en el cuerpo de la solicitud de una llamada a messages.send, como se muestra en los siguientes ejemplos.

Java

gmail/snippets/src/main/java/SendMessage.java
import com.google.api.client.googleapis.json.GoogleJsonError;
import com.google.api.client.googleapis.json.GoogleJsonResponseException;
import com.google.api.client.http.HttpRequestInitializer;
import com.google.api.client.http.javanet.NetHttpTransport;
import com.google.api.client.json.gson.GsonFactory;
import com.google.api.services.gmail.Gmail;
import com.google.api.services.gmail.GmailScopes;
import com.google.api.services.gmail.model.Message;
import com.google.auth.http.HttpCredentialsAdapter;
import com.google.auth.oauth2.GoogleCredentials;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.util.Properties;
import javax.mail.MessagingException;
import javax.mail.Session;
import javax.mail.internet.InternetAddress;
import javax.mail.internet.MimeMessage;
import org.apache.commons.codec.binary.Base64;

/* Class to demonstrate the use of Gmail Send Message API */
public class SendMessage {
  /**
   * Send an email from the user's mailbox to its recipient.
   *
   * @param fromEmailAddress - Email address to appear in the from: header
   * @param toEmailAddress   - Email address of the recipient
   * @return the sent message, {@code null} otherwise.
   * @throws MessagingException - if a wrongly formatted address is encountered.
   * @throws IOException        - if service account credentials file not found.
   */
  public static Message sendEmail(String fromEmailAddress,
                                  String toEmailAddress)
      throws MessagingException, IOException {
        /* Load pre-authorized user credentials from the environment.
           TODO(developer) - See https://developers.google.com/identity for
            guides on implementing OAuth2 for your application.*/
    GoogleCredentials credentials = GoogleCredentials.getApplicationDefault()
        .createScoped(GmailScopes.GMAIL_SEND);
    HttpRequestInitializer requestInitializer = new HttpCredentialsAdapter(credentials);

    // Create the gmail API client
    Gmail service = new Gmail.Builder(new NetHttpTransport(),
        GsonFactory.getDefaultInstance(),
        requestInitializer)
        .setApplicationName("Gmail samples")
        .build();

    // Create the email content
    String messageSubject = "Test message";
    String bodyText = "lorem ipsum.";

    // Encode as MIME message
    Properties props = new Properties();
    Session session = Session.getDefaultInstance(props, null);
    MimeMessage email = new MimeMessage(session);
    email.setFrom(new InternetAddress(fromEmailAddress));
    email.addRecipient(javax.mail.Message.RecipientType.TO,
        new InternetAddress(toEmailAddress));
    email.setSubject(messageSubject);
    email.setText(bodyText);

    // Encode and wrap the MIME message into a gmail message
    ByteArrayOutputStream buffer = new ByteArrayOutputStream();
    email.writeTo(buffer);
    byte[] rawMessageBytes = buffer.toByteArray();
    String encodedEmail = Base64.encodeBase64URLSafeString(rawMessageBytes);
    Message message = new Message();
    message.setRaw(encodedEmail);

    try {
      // Create send message
      message = service.users().messages().send("me", message).execute();
      System.out.println("Message id: " + message.getId());
      System.out.println(message.toPrettyString());
      return message;
    } catch (GoogleJsonResponseException e) {
      // TODO(developer) - handle error appropriately
      GoogleJsonError error = e.getDetails();
      if (error.getCode() == 403) {
        System.err.println("Unable to send message: " + e.getDetails());
      } else {
        throw e;
      }
    }
    return null;
  }
}

Python

gmail/snippet/send mail/send_message.py
from __future__ import print_function

import base64
from email.message import EmailMessage

import google.auth
from googleapiclient.discovery import build
from googleapiclient.errors import HttpError


def gmail_send_message():
    """Create and send an email message
    Print the returned  message id
    Returns: Message object, including message id

    Load pre-authorized user credentials from the environment.
    TODO(developer) - See https://developers.google.com/identity
    for guides on implementing OAuth2 for the application.
    """
    creds, _ = google.auth.default()

    try:
        service = build('gmail', 'v1', credentials=creds)
        message = EmailMessage()

        message.set_content('This is automated draft mail')

        message['To'] = 'gduser1@workspacesamples.dev'
        message['From'] = 'gduser2@workspacesamples.dev'
        message['Subject'] = 'Automated draft'

        # encoded message
        encoded_message = base64.urlsafe_b64encode(message.as_bytes()) \
            .decode()

        create_message = {
            'raw': encoded_message
        }
        # pylint: disable=E1101
        send_message = (service.users().messages().send
                        (userId="me", body=create_message).execute())
        print(F'Message Id: {send_message["id"]}')
    except HttpError as error:
        print(F'An error occurred: {error}')
        send_message = None
    return send_message


if __name__ == '__main__':
    gmail_send_message()

Si intentas enviar una respuesta y quieres que el correo electrónico se converse, asegúrate de lo siguiente:

  1. Los encabezados Subject coinciden
  2. Los encabezados References y In-Reply-To siguen el estándar RFC 2822.

Para obtener información sobre cómo enviar un mensaje desde un borrador, consulta Cómo crear borradores.