This article demonstrates building a Gmail app using the Gmail JavaScript API, extending a previous example to include email sending, composing, and replying. No prior knowledge of the previous article is required. The complete source code is available on GitHub (folder 02 - Sending mail).

Key Features:

• Utilizes the Gmail JavaScript API for reading, composing, and replying to emails.
• Requires setting up a Google Developer Console project and generating API key and OAuth client ID credentials.
• Needs 'http://www.miracleart.cn/link/244e6b76cb404f1e057b6417e1c7eab5' and 'http://www.miracleart.cn/link/ef1f3fc8be928fd5b5e721689bb92b7b' scopes for sending emails.
• Sends emails using the Users.messages: send endpoint, constructing RFC 5322 compliant messages.
• While direct email scheduling isn't supported, Google Apps Script can be used for timed email delivery.

Setting Up the Gmail API:

1. Create a Google Developer Console project.
2. Generate a browser API key (consider adding HTTP referrers for production).
3. Generate an OAuth client ID for a web application, specifying authorized JavaScript origins (e.g., http://localhost). A redirect URI is not needed.

Application Setup:

1. Clone the example code: git clone git@github.com:sitepoint-editors/gmail-api-javascript-example.git
2. In index.html, replace placeholders with your API key and client ID.
3. Update the scopes variable in index.html to include 'http://www.miracleart.cn/link/ef1f3fc8be928fd5b5e721689bb92b7b'.

Sending Emails:

A "Compose" button is added to the UI, opening a modal for composing emails. The sendEmail() function handles submission, disabling the send button during the asynchronous operation to prevent multiple submissions. The sendMessage() function interacts with the Gmail API, constructing the RFC 5322 message (including headers) and base64 encoding it before sending. The composeTidy() function cleans up the modal after successful sending.

Replying to Emails:

A "Reply" button is added to the message view modal. The fillInReply() function populates a reply modal with recipient, subject (prefixed with "Re:"), and Message-ID for proper threading. The sendReply() function sends the reply, using the In-Reply-To header. replyTidy() cleans up the reply modal.

Further Improvements and Features:

• Staggered authorization requests (read-only initially, then send permission).
• Improved "To" field in the compose modal (name and email).
• Auto-complete for the "To" field using contact lists.
• Email forwarding.
• CC and BCC support.
• Full header viewing.
• HTML email support with WYSIWYG editor.

Frequently Asked Questions (FAQs):

The article concludes with a FAQ section covering topics such as sending emails with attachments, multiple recipients, scheduling (using Google Apps Script), HTML emails, error handling, custom headers, authentication, emojis, inline images, and quota monitoring. These FAQs provide concise answers and point to relevant techniques.

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