Sending Email Gmail API

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

Emails are sent as base64url encoded strings within the raw property of amessage 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.sendto 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 withRFC 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 MimeMessageclass 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 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;
}
}

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

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

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 /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’] = ” message[‘From’] = ” message[‘Subject’] = ‘Automated draft’ # encoded message encoded_message = base64.urlsafe_b64encode(message.as_bytes()).decode() create_message = { ‘message’: { ‘raw’: encoded_message } } # pylint: disable=E 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 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 /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 Messageresource.

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 /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’] = ” mime_message[‘From’] = ” 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=E 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 tomessages.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.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 /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 /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’] = ” message[‘From’] = ” message[‘Subject’] = ‘Automated draft’ # encoded message encoded_message = base64.urlsafe_b64encode(message.as_bytes()) \ .decode() create_message = { ‘raw’: encoded_message } # pylint: disable=E 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 theRFC 2822 standard.

For information on sending a message from a draft, seeCreating Drafts.