Build an n8n Form-to-Newsletter Workflow with GPT-4o, Email Approval, and SendGrid

Form input → GPT-4o generates Markdown newsletter → email preview approval → convert to HTML and send via SendGrid

Who

Digital marketers, content creators, community managers, and small teams sending regular newsletters

You get

Collect brief requirements via n8n form, auto-generate a Markdown newsletter with subject line using GPT-4o, send a Gmail preview for human approval, then convert to HTML and distribute to subscribers via SendGrid

You need

n8n · gmail · google-sheets · openai · sendgrid

Steps

1. Configure credentials and environment

   Set up credentials for OpenAI, Google (Sheets & Gmail), and SendGrid in n8n. Ensure your n8n version supports LangChain nodes.

2. Set the subscriber list

   Open the Workflow Configuration node (Set node). Replace the subscriber_list placeholder with your comma-separated subscriber emails. Keep includeOtherFields as true to pass through form data.

3. Configure Google Sheets logging

   Create a Google Sheet with columns for topic, target, sender, and admin_email. In the Store Form Responses node, enter your Document ID and Sheet Name; leave mappingMode as autoMapInputData.

4. Configure the AI content generation node

   The Generate Newsletter Content node uses define mode, connected to OpenAI GPT-4o Model and JSON Output Parser. Verify the text parameter passes topic, target, and sender variables; the options.systemMessage is the system prompt requiring JSON output with subject and body_markdown only.

   Execution prompt · Source text。Generate Newsletter Content node text parameter (user message input)

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   =トピック: {{ $json.topic }}
   ターゲット読者層: {{ $json.target }}
   送信者名: {{ $json.sender }}

   Execution prompt · Source text。Generate Newsletter Content node options.systemMessage parameter

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   あなたはプロのメールマーケターです。入力されたトピックとターゲット読者層に基づいて、魅力的なメルマガを作成してください。
   
   タスク:
   1. ターゲット読者層に響く件名を作成する
   2. トピックに基づいた本文をMarkdown形式で作成する
   3. HTMLタグは使用せず、Markdownのみを使用する
   4. 本文は読みやすく、価値のある情報を提供する内容にする
   5. JSONフォーマットで出力する（subject と body_markdown のみ）
   
   注意事項:
   - 余計な会話や説明は含めない
   - JSONのみを出力する
   - Markdownは見出し、リスト、強調などを適切に使用する

   Execution prompt · Source text。JSON Output Parser node inputSchema parameter

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   {
   	"type": "object",
   	"properties": {
   		"subject": {
   			"type": "string",
   			"description": "Email subject line that captures attention"
   		},
   		"body_markdown": {
   			"type": "string",
   			"description": "Newsletter body content in Markdown format"
   		}
   	}
   }

5. Configure approval email and wait node

   The Convert Markdown to HTML node transforms body_markdown to HTML. The Send Approval Email node (Gmail) sends a preview with an approval link using $execution.resumeUrl to admin_email. The Wait for Approval node uses webhook resume mode with resumeAmount set to 24 hours.

   Execution prompt · Source text。Send Approval Email node message parameter (HTML email body)

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   =<h2>メルマガ承認依頼</h2>
   <p>以下の内容で承認をお願いします。</p>
   
   <h3>件名プレビュー:</h3>
   <p><strong>{{ $json.subject }}</strong></p>
   
   <h3>本文プレビュー:</h3>
   <div style="border: 1px solid #ccc; padding: 15px; margin: 10px 0;">
   {{ $json.data }}
   </div>
   
   <h3>送信者情報:</h3>
   <p>送信者名: {{ $('Workflow Configuration').first().json.sender }}</p>
   <p>ターゲット: {{ $('Workflow Configuration').first().json.target }}</p>
   
   <hr>
   <p><a href="{{ $execution.resumeUrl }}" style="background-color: #4CAF50; color: white; padding: 10px 20px; text-decoration: none; border-radius: 5px; display: inline-block;">✅ 承認して配信する</a></p>
   <p><small>※このリンクは24時間有効です。クリックすると即座に配信が開始されます。</small></p>

6. Configure SendGrid delivery and test

   In the Send Newsletter to Subscribers node, replace fromEmail with your SendGrid verified sender address. subject, toEmail, fromName, and contentValue reference upstream nodes via expressions. Click Test Workflow, fill out the Form Trigger URL, check your email for the approval draft, and click the link to complete the flow.

You are an n8n workflow setup assistant. The user wants to replicate an AI newsletter generation and approval workflow. Help them:
1. Confirm they have OpenAI, Google Cloud, and SendGrid credentials ready;
2. Configure the Set node subscriber list, Google Sheets document ID, and SendGrid sender email in order;
3. If they want to change the AI tone, guide them to edit the systemMessage in the Generate Newsletter Content node;
4. When testing, remind them to check spam folders and note the 24-hour expiry on the approval link.
Do not perform sends on their behalf; only provide configuration guidance.