Best AI Models for Email Writing

What We Looked At

• Tone variety
• Subject line quality
• Personalization ability
• Bulk generation
• Professional vs casual range

Choosing the right tone

Cold sales emails and executive briefings sit at opposite ends of a spectrum, and most AI models handle one better than the other. GPT-4o writes punchy, direct outreach that doesn't sound like it came from a template. Claude writes careful, precise correspondence that holds up to scrutiny from a senior reader. The practical tip: always specify the recipient's role, what you want them to do, and the relationship context — the AI can't infer these from the subject line alone.

Generating subject line variants

Subject lines are one of the highest-leverage AI tasks in email. Ask GPT-4o for 20 variants — give it the product, the audience, and the goal — and you'll get subject lines spanning curiosity, urgency, value, specificity, and social proof. You'd naturally write three or four; AI gives you a wider range to test from. Running A/B tests on AI-generated subject lines has consistently produced 15–30% lift in open rates for teams we've spoken with.

Bulk email at scale

For high-volume sequences — onboarding, outreach, newsletters — GPT-4o mini does most of what you need at a fraction of the cost. Set up a consistent system prompt that captures your brand voice, then pass each email's brief (recipient segment, key message, CTA) as the user message. At $0.15/1M tokens, you're generating thousands of personalised drafts for cents. The time cost at that point is review and editing, not generation.