Restflow.io

## Introduction

In email marketing, the subject line plays a critical role in determining open rates and overall campaign success. Marketing teams continuously test and optimize subject lines to improve engagement, but analyzing subject line performance manually across multiple campaigns and emails is time-consuming and error-prone.

This article demonstrates how to build an automated workflow using n8n to analyze subject line performance automatically. This automation benefits marketing teams, email specialists, and growth hackers by providing real-time insights into subject line open rates and engagement metrics, enabling faster and data-driven decisions.

The workflow integrates the following tools/services:

– Gmail or any SMTP email provider (for sending emails)
– SendGrid (or similar ESP with API access for email engagement metrics)
– Google Sheets (to log and analyze data)
– Slack (optional, for performance alerts)

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## Use Case Overview

Marketing teams often send multiple campaigns with diverse subject lines and want to evaluate which phrasing or personalization drives higher open rates. This workflow automatically fetches email engagement data (opens, clicks) from the SendGrid API, aggregates the data by subject line, stores it in Google Sheets, and sends a summary notification to Slack for quick insights.

By automating this, marketers avoid manual data export and complex spreadsheet formulas.

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## Technical Tutorial

### Prerequisites

– An n8n instance (self-hosted or n8n.cloud account)
– SendGrid account with API key and email campaigns sent via SendGrid
– Google account with access to Google Sheets and Google Drive
– Slack workspace (optional for notification integration)

### Step 1: Create a Google Sheet for Data Storage

Set up a Google Sheet with the following columns:

| Campaign ID | Subject Line | Sent Count | Open Count | Click Count | Open Rate (%) | Click Rate (%) | Date |

This sheet will be used to log metrics for each campaign or batch of emails.

### Step 2: Set up n8n Workflow

Open n8n and create a new workflow titled “Email Subject Line Performance Analysis”.

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### Step 3: Define the Trigger

Use the **Cron node** to schedule this workflow to run daily at midnight, or adjust to your reporting cadence.

– Node Name: Cron
– Settings: Every day at 00:00

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### Step 4: Fetch Email Campaigns Data from SendGrid

Use the **HTTP Request node** to call the SendGrid API that lists email campaigns and their engagement stats.

– Node Name: Get Campaign Metrics
– HTTP Method: GET
– URL: `https://api.sendgrid.com/v3/campaigns`
– Headers:
– Authorization: Bearer `{{SENDGRID_API_KEY}}`
– Content-Type: application/json

Once the campaigns are retrieved, make additional API calls to fetch statistics for each campaign:

– Use the flow’s SplitInBatches node or function node to iterate campaigns.
– For each campaign, call:
– GET `https://api.sendgrid.com/v3/campaigns/{campaign_id}/stats`

Extract the following from stats response:

– subject line
– emails sent
– unique opens
– unique clicks

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### Step 5: Calculate Open and Click Rates

Within a **Function node**, calculate the rates:

“`javascript
return items.map(item => {
const sent = item.json.sent;
const opens = item.json.opens;
const clicks = item.json.clicks;
item.json.open_rate = sent > 0 ? (opens / sent) * 100 : 0;
item.json.click_rate = sent > 0 ? (clicks / sent) * 100 : 0;
item.json.date = new Date().toISOString().split(‘T’)[0];
return item;
});
“`

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### Step 6: Update Google Sheets with Metrics

Use the **Google Sheets node** to append the calculated data to your pre-created sheet.

– Set Operation to Append
– Map fields correctly to the columns:
– Campaign ID
– Subject Line
– Sent Count
– Open Count
– Click Count
– Open Rate (%)
– Click Rate (%)
– Date

Use OAuth2 credentials for authorization.

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### Step 7 (Optional): Notify Marketing Team via Slack

If you want alerts about top performing or underperforming subject lines,

– Add a **IF node** to check if open_rate < threshold (for example 15%). - If true, use Slack node to send a message to the #marketing-alerts channel with details. Example message template: ``` Subject Line Performance Alert: Subject: {{ $json["subject_line"] }} Open Rate: {{ $json["open_rate"] }}% Campaign ID: {{ $json["campaign_id"] }} Check the Google Sheet for details. ``` --- ### Step 8: Error Handling and Robustness - Use a **Error Trigger** node to catch workflow or API call failures and notify your team. - Add retry logic in HTTP Request nodes with exponential backoff to handle transient API errors. - Validate API responses and check for empty data to avoid writing incomplete data. - Store logs for each run. Use Google Sheets or an external logging system. --- ### Step 9: Enhancements and Scaling - Adapt the workflow to support other ESPs like Mailchimp, HubSpot, or Amazon SES by replacing API calls accordingly. - Add A/B testing analysis by comparing subject lines side-by-side based on performance data. - Integrate visualization tools like Google Data Studio or Power BI by exporting summarized metrics. - Scale to handle multiple SendGrid subusers or accounts by looping credentials and appending account identifiers. --- ## Summary This guide showed how to automate the collection and analysis of email subject line performance using n8n, SendGrid, Google Sheets, and Slack. Automating subject line metrics frees marketing teams from tedious manual reporting and speeds up optimization cycles. By scheduling daily data pulls, calculating meaningful KPIs, and centralizing results in an accessible sheet, you enable faster, data-driven decisions that can significantly improve email engagement. --- ## Bonus Tip To improve the accuracy of your analysis, consider enriching your workflow to normalize data for audience size, time of send, and segment differences. Incorporate campaign metadata from your CRM to correlate subject line performance with customer lifetime value or conversion rates, creating a holistic email marketing performance dashboard.