Use HubSpot's AI Email Writer and Content Assistant

1. In the Subject line field, click the AI icon (appears when you focus the field)
2. Enter context: what's in the email, who's receiving it, one key benefit
3. HubSpot generates 3-5 subject line options
4. Click to insert the one you want (edit further as needed)

Pro tip: Generate subject lines after writing the email body, not before — the AI will have more context about what the email actually says and generate more accurate subject lines.

HubSpot's Smart Content feature (Professional and above) lets you show different email content to different contact segments without building separate emails:

1. Select any content block in the email editor
2. Click Smart content in the block settings
3. Define rules (e.g., "Show this block only to contacts with lifecycle stage = Lead")
4. Create an alternate version for that segment
5. HubSpot serves the correct version to each contact at send time

Combine with AI: Generate the base content with AI, then use Smart Content to show segment-specific versions of the hero block or CTA without rewriting the entire email.