建立及傳送電子郵件

本文說明如何使用 Gmail API 建立及傳送電子郵件。

使用 Gmail API 傳送電子郵件的方法有兩種：

• 您可以使用 messages.send 方法直接傳送。
• 您可以使用 drafts.send 方法，從草稿傳送訊息。如要進一步瞭解如何傳送草稿訊息，請參閱「傳送草稿」。

Gmail 郵件會以 base64URL 編碼字串的形式，在 messages 資源的 raw 欄位中傳送。如要傳送電子郵件，請按照下列步驟操作：

1. 建立電子郵件內容，並以 base64URL 字串編碼。
2. 建立新的訊息資源，並將其 raw 屬性設為您剛建立的 base64URL 字串。
3. 呼叫 messages.send 方法，或在傳送草稿時呼叫 drafts.send 方法，即可傳送訊息。

這個工作流程的詳細資料會因您選擇的用戶端程式庫和程式設計語言而異。

建立訊息

Gmail API 規定 MIME 電子郵件必須符合 RFC 2822 規範，並編碼為 base64URL 字串。許多程式設計語言都有程式庫或公用程式，可簡化建立及編碼 MIME 訊息的程序。

下列程式碼範例說明如何使用各種語言的 Google API 用戶端程式庫建立 MIME 訊息：

Java

您可以使用 javax.mail.internet 套件中的 MimeMessage 類別，簡化電子郵件訊息的建立程序。下列程式碼範例說明如何建立電子郵件訊息，包括標頭：

gmail/snippets/src/main/java/CreateEmail.java

前往 GitHub 查看

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;
  }
}

接著，請編碼 MimeMessage、例項化 messages 物件，並將 base64URL 編碼的訊息字串設為 raw 屬性的值。

gmail/snippets/src/main/java/CreateMessage.java

前往 GitHub 查看

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

下列程式碼範例說明如何建立 MIME 訊息、將其編碼為 base64URL 字串，並指派給 messages 資源的 raw 欄位：

gmail/snippet/send mail/create_draft.py

前往 GitHub 查看

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"] = "[e-mail]"
    message["From"] = "[e-mail]"
    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()

cURL

curl --request POST \
  'https://gmail.googleapis.com/gmail/v1/users/me/drafts' \
  --header 'Authorization: Bearer ACCESS_TOKEN' \
  --header 'Accept: application/json' \
  --header 'Content-Type: application/json' \
  --data '{"message":{"raw":"MESSAGE"}}'

更改下列內容：

• ACCESS_TOKEN：授予 API 存取權的存取權杖。
• MESSAGE：採用 RFC 2822 格式的 MIME 訊息，並以 base64URL 編碼。

建立含有附件的訊息

建立含附件的郵件與建立任何其他郵件類似，但將檔案上傳為多部分 MIME 郵件的程序取決於程式設計語言。

下列程式碼範例顯示建立含有附件的多部分 MIME 訊息的可能方式：

Java

以下程式碼範例說明如何建立多部分 MIME 訊息。編碼和指派步驟與建立訊息相同。

gmail/snippets/src/main/java/CreateDraftWithAttachment.java

前往 GitHub 查看

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

與建立訊息範例類似，這個範例也會處理將訊息編碼為 base64URL，並將其指派給 messages 資源的 raw 欄位。

gmail/snippet/send mail/create_draft_with_attachment.py

前往 GitHub 查看

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"] = "[e-mail]"
    mime_message["From"] = "[e-mail]"
    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()

cURL

curl --request POST \
  'https://gmail.googleapis.com/gmail/v1/users/me/drafts' \
  --header 'Authorization: Bearer ACCESS_TOKEN' \
  --header 'Accept: application/json' \
  --header 'Content-Type: application/json' \
  --data '{"message":{"raw":"MESSAGE"}}'

更改下列內容：

• ACCESS_TOKEN：授予 API 存取權的存取權杖。
• MESSAGE：包含附件的 RFC 2822 格式 MIME 訊息，以 base64URL 編碼。

傳送訊息

建立訊息後，您可以在 messages.send 方法的要求主體中提供訊息，即可傳送訊息，如下列範例所示：

Java

gmail/snippets/src/main/java/SendMessage.java

前往 GitHub 查看

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

前往 GitHub 查看

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"] = "[e-mail]"
    message["From"] = "[e-mail]"
    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()

cURL

curl --request POST \
  'https://gmail.googleapis.com/gmail/v1/users/me/messages/send' \
  --header 'Authorization: Bearer ACCESS_TOKEN' \
  --header 'Accept: application/json' \
  --header 'Content-Type: application/json' \
  --data '{"raw":"MESSAGE"}'

更改下列內容：

• ACCESS_TOKEN：授予 API 存取權的存取權杖。
• MESSAGE：採用 RFC 2822 格式的 MIME 訊息，並以 base64URL 編碼。

如要回覆郵件並將其歸入討論串，請確認下列事項：

1. Subject 標頭相符
2. References 和 In-Reply-To 標頭符合 RFC 2822 標準。

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