Sending Email

There are two ways to send email using the Gmail API:

Emails are sent as base64url encoded strings within the raw property of a message resource. The high-level workflow to send an email is to:

  1. Create the email content in some convenient way and encode it as a base64url string.
  2. Create a new message resource and set its raw property to the base64url string you just created.
  3. Call messages.send, or, if sending a draft, drafts.send to send the message.

The details of this workflow can vary depending on your choice of client library and programming language.

Creating messages

The Gmail API requires MIME email messages compliant with RFC 2822 and encoded as base64url strings. Many programming languages have libraries or utilities that simplify the process of creating and encoding MIME messages. The following code examples demonstrate how to create a MIME message using the Google APIs client libraries for various languages.

Java

Creating an email message can be greatly simplified with the MimeMessage class in the javax.mail.internet package. The following example shows how to create the email message, including the headers:

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

/* 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;
    }
}

The next step is to encode the MimeMessage, instantiate a Message object, and set the base64url encoded message string as the value of the raw property.

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

/* 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

The following code sample demonstrates creating a MIME message, encoding to a base64url string, and assigning it to the raw field of the Message resource:

gmail/snippet/send mail/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 = {
                '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()

Creating messages with attachments

Creating a message with an attachment is like creating any other message, but the process of uploading the file as a multi-part MIME message depends on the programming language. The following code examples demonstrate possible ways of creating a multi-part MIME message with an attachment.

Java

The following example shows how to create a multi-part MIME message, the encoding and assignment steps are the same as above.

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 org.apache.commons.codec.binary.Base64;

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 java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.IOException;
import java.util.Collections;
import java.util.Properties;

/* 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

Similar to the previous example, this example also handles encoding the message to base64url and assigning it to the raw field of the Message resource.

gmail/snippet/send mail/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 = {
            '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()

Sending messages

Once you have created a message, you can send it by supplying it in the request body of a call to messages.send, as demonstrated in the following examples.

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.GmailScopes;
import com.google.auth.http.HttpCredentialsAdapter;
import com.google.auth.oauth2.GoogleCredentials;
import org.apache.commons.codec.binary.Base64;
import com.google.api.services.gmail.Gmail;
import com.google.api.services.gmail.model.Message;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.util.Collections;
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 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()

If you're trying to send a reply and want the email to thread, make sure that:

  1. The Subject headers match
  2. The References and In-Reply-To headers follow the RFC 2822 standard.

For information on sending a message from a draft, see Creating Drafts.