Use HubSpot AI to Generate and Test Email Subject Lines

What This Does

HubSpot's built-in AI generates alternative email subject lines directly in the email creation flow — no need to leave HubSpot or open a separate AI tool — and lets you set up A/B tests between your original and the AI-generated options.

Before You Start

• You have a HubSpot account with email marketing access (Starter plan or above)
• You're creating or editing a marketing email in HubSpot
• Your email body copy is drafted (the AI uses it to generate relevant subject lines)

Steps

1. Open or create your email in HubSpot

In HubSpot, go to Marketing → Email → Create email. Choose your email type (regular or automated) and select a template, or open an existing email draft.

What you should see: The HubSpot email editor with a toolbar on the left and your email preview on the right.

2. Navigate to the Subject Line field

In the email editor, look at the Settings tab (usually in the left panel) or click directly on the "Subject line" field at the top of the editor.

What you should see: The subject line input field with your current subject line text.

3. Use "Generate with AI"

Next to the subject line field, look for a small sparkle icon (✨) or a button labeled "Generate with AI." Click it.

HubSpot will read your email body content and generate 3–5 subject line suggestions tailored to what your email is actually about.

What you should see: A dropdown or panel showing 3–5 generated subject line options.

Troubleshooting: If the sparkle icon isn't visible, make sure your email body has content — the AI needs something to generate from. Also check that you're on an eligible HubSpot plan (some AI features require Marketing Hub Starter or above).

4. Select or customize a suggestion

Click any suggestion to apply it to the subject line field. You can edit it directly after inserting — the AI output is a starting point, not a final answer.

To set up an A/B test: After selecting your AI-generated subject line as Option A, click "Run an A/B test" → add your original (or another AI option) as Option B → set the test split (typically 50/50 or 70/30) → set the winner criteria (open rate or click rate).

What you should see: Your email now shows two subject line variants ready for A/B testing.

5. Send and review results

Send the campaign normally. After 4–8 hours (or when your test duration completes), check the A/B test results in the email performance dashboard. HubSpot will automatically send the winning version to the remaining list if you configure it that way.

Real Example

Scenario: You've written an email promoting a new customer success case study for a B2B software client. Your original subject line: "New Case Study: How Acme Corp Saved Time with Our Platform."

What you do: In HubSpot email editor → click sparkle icon next to subject line → "Generate with AI."

What you get:

• "How Acme Corp cut reporting time by 40% (new case study)"
• "The 3 things Acme did differently — and what it means for your team"
• "Inside Acme Corp's before and after"

Run an A/B test between your original and the most compelling AI option.

Tips

• The AI-generated options are typically shorter and more benefit-focused than what most copywriters write under time pressure — test them even if your original feels strong.
• If HubSpot's generated options feel generic, edit your email's preview text to be more specific before regenerating — the AI uses the preview text as context too.
• Review open rate results at 4 hours minimum; for smaller lists (under 1,000), wait 24–48 hours for statistical significance.

Tool interfaces change — if a button has moved, look for similar AI/magic/smart options in the same menu area.