Best AI for Email Writing: We Tested ChatGPT, Claude, and Gemini With the Same Prompts
AI-generated emails have a reputation problem: they sound robotic, overly formal, and painfully obvious. We tested ChatGPT, Claude, and Gemini on 5 common email types to answer one question: Which AI writes the best emails in 2026?
You've probably received one. Subject line: "Following up." Opening line: "I hope this email finds you well." Body: three paragraphs that say nothing in 200 words.
But here's the truth: the problem isn't AI—it's the prompt and the model you're using.
Here's what we found—and how to make AI emails sound human.
Why AI Emails Sound Robotic (And How to Fix It)
Most AI-generated emails fail for two reasons:
1. Vague Prompts
When you tell ChatGPT "write a follow-up email," it defaults to the safest, most generic template possible.
Bad prompt:
"Write a follow-up email."
AI output: A formal, robotic message that screams "I used AI."
Good prompt:
"Write a 100-word follow-up email to a client who requested a demo last week but hasn't responded. Tone: friendly but not pushy. Include one specific value proposition (saves 10 hours/week). End with a low-pressure CTA to book a 15-minute call."
AI output: A natural, conversational email that gets replies.
2. Wrong Model for the Job
Not all AI models write emails the same way:
- ChatGPT writes professional, structured emails (great for B2B)
- Claude writes conversational, empathetic emails (great for customer support)
- Gemini writes formal, data-driven emails (great for reports/summaries)
Using ChatGPT for a warm, personal email is like wearing a suit to a beach party. Technically appropriate, but wildly out of place.
Our Testing Framework: 5 Email Types
We tested each AI model on these common email scenarios:
- Cold outreach (B2B sales email)
- Follow-up (after no response to a demo request)
- Customer support (handling a refund request)
- Internal team communication (project update to colleagues)
- Networking (reaching out to a potential mentor)
Each AI received the exact same A+ grade prompt to ensure fair comparison.
Test 1: Cold Outreach Email (B2B Sales)
Prompt:
"Write a 150-word cold email to marketing directors at mid-size B2B companies. Pitch our AI-powered analytics tool. Highlight one key benefit: reduces reporting time by 80%. Tone: professional but conversational. End with a CTA to book a 15-minute demo."
ChatGPT Result
Subject: Cut Your Reporting Time by 80%
Body:
Hi [Name],
I know marketing reports are eating up hours of your week. What if you could cut that time by 80%?
Our AI-powered analytics tool automates your reporting workflow so you can focus on strategy instead of spreadsheets. Teams using [Product] save an average of 12 hours per week.
Would you be open to a quick 15-minute call to see if it's a fit for your team? No pressure—just a chance to show you how it works.
Let me know what works for your calendar.
Best,
[Your Name]
Strengths:
- Professional and concise
- Clear value proposition
- Strong subject line
- Non-pushy CTA
Weaknesses:
- Slightly formal
- "[Product]" placeholder feels generic
Grade: A – Solid B2B outreach email.
Claude Result
Subject: Your weekly reporting: 12 hours → 2 hours
Body:
Hey [Name],
I'm guessing you're spending way too much time pulling marketing reports (I've been there).
Quick question: what would you do with an extra 12 hours a week?
Our tool handles all the data aggregation, formatting, and visualization automatically. Your team gets beautiful reports without the manual work.
Want to see it in action? I can walk you through a quick demo—15 minutes, no commitment.
Sound interesting?
[Your Name]
Strengths:
- Very conversational and personable
- Great subject line (specific numbers)
- Engaging opening question
- Natural, human tone
Weaknesses:
- Might be too casual for some industries
Grade: A – Best for creative/casual industries.
Gemini Result
Subject: AI Analytics Solution for Marketing Teams
Body:
Dear [Name],
I am reaching out to introduce our AI-powered analytics platform designed for marketing teams. Our solution reduces reporting time by 80% through automated data aggregation and visualization.
Key features include:
- Real-time dashboard integration
- Automated report generation
- Customizable metrics tracking
I would appreciate the opportunity to schedule a 15-minute demonstration to discuss how our platform can benefit your team.
Please let me know your availability.
Best regards,
[Your Name]
Strengths:
- Very professional
- Clear feature list
Weaknesses:
- Stiff and formal
- "Dear [Name]" and "I am reaching out" are red flags for spam filters
- Reads like a 2010 sales email
- No personality
Grade: C+ – Too robotic for modern B2B outreach.
Winner for cold outreach: Claude (best balance of professional and human)
Test 2: Follow-Up Email (After No Response)
Prompt:
"Write a 100-word follow-up email to a client who requested a demo 5 days ago but hasn't responded to schedule it. Tone: friendly, not pushy. Include one new piece of value (case study showing 3x ROI). End with a low-pressure out."
ChatGPT Result
Hi [Name],
I wanted to follow up on the demo you requested last week. I know things get busy—no worries if now's not the right time.
In case it's helpful, I just published a case study showing how [Similar Company] achieved 3x ROI in their first quarter using our tool.
If you'd still like to see a demo, I'm happy to find a time that works. Otherwise, feel free to reach out whenever you're ready.
Best,
[Your Name]
Grade: A – Professional, not pushy, includes value.
Claude Result
Hey [Name],
Just circling back on the demo—totally understand if it's gotten buried in your inbox (happens to me all the time).
Quick heads up: we just wrapped a case study with a team like yours. They saw 3x ROI in Q1. Happy to send it over if you're curious.
Still interested in a demo? If not, no worries—just let me know.
Cheers,
[Your Name]
Grade: A+ – Extremely natural, empathetic, zero pressure.
Gemini Result
Dear [Name],
I am following up regarding your demo request from February 14th. We have not yet received confirmation of your availability.
I wanted to share a recent case study demonstrating 3x ROI for a client in your industry. Please let me know if you remain interested in scheduling a demonstration.
Thank you,
[Your Name]
Grade: D – Reads like an automated reminder. Too formal and impersonal.
Winner for follow-up: Claude (most human and empathetic)
Test 3: Customer Support Email (Refund Request)
Prompt:
"Write a 120-word customer support email responding to a refund request. Customer paid $50 for a monthly subscription but wants a refund because they didn't use it. Company policy: refunds within 30 days. Tone: empathetic and helpful."
ChatGPT Result
Hi [Name],
Thanks for reaching out. I'm sorry to hear the subscription didn't work out for you this month.
Good news: you're well within our 30-day refund window, so I've processed your refund for $50. You should see it back in your account within 3-5 business days.
If you ever want to give it another try, you're always welcome back. No hard feelings!
Is there anything else I can help with today?
Best,
[Your Name]
Grade: A – Clear, helpful, empathetic.
Claude Result
Hey [Name],
I totally get it—life gets busy and sometimes subscriptions slip through the cracks.
I just processed your $50 refund. It should hit your account in 3-5 business days. All set!
If you want to come back anytime, we'll be here. And if there's anything we could've done better, I'd love to hear it.
Thanks for giving us a shot!
[Your Name]
Grade: A+ – Warm, understanding, and genuinely helpful.
Gemini Result
Dear [Name],
Thank you for contacting customer support. I have reviewed your refund request for the $50 monthly subscription.
As you are within our 30-day refund policy window, I have initiated the refund process. The refund will be credited to your original payment method within 3-5 business days.
Please let me know if you require further assistance.
Sincerely,
[Your Name]
Grade: B – Accurate but impersonal. Sounds like a script.
Winner for customer support: Claude (most empathetic and human)
Test 4: Internal Team Email (Project Update)
Prompt:
"Write a 150-word email to your team updating them on a project deadline change. Original deadline: Friday. New deadline: next Wednesday. Reason: waiting on client feedback. Tone: clear and collaborative."
ChatGPT Result
Hey team,
Quick update on the [Project Name] deadline. We're pushing it from this Friday to next Wednesday.
Reason: We're still waiting on final feedback from the client. Rather than rush ahead and risk rework, let's use the extra time to tighten up our deliverables.
Here's the updated timeline:
- Client feedback: by Monday
- Final revisions: Tuesday
- Delivery: Wednesday morning
This gives us breathing room to get it right the first time. Let me know if you have any questions or concerns.
Thanks for your flexibility!
[Your Name]
Grade: A – Clear, organized, collaborative tone.
Claude Result
Hey all,
Heads up: we're moving the [Project] deadline from Friday to next Wednesday.
Short version: still waiting on the client's feedback. Rather than guessing what they want, let's use the extra time to polish everything.
New plan:
- Feedback in by Monday
- Revisions Tuesday
- Ship Wednesday AM
Silver lining: we can actually get this right instead of rushing. Hit me up if you need anything.
Appreciate you all rolling with it!
[Your Name]
Grade: A – Conversational, team-friendly, positive framing.
Winner for internal email: Tie between ChatGPT and Claude (both clear and collaborative)
Test 5: Networking Email (Reaching Out to a Mentor)
Prompt:
"Write a 150-word networking email to a senior product manager you admire. You're a junior PM looking for career advice. Tone: respectful but not overly formal. Include one specific reason you're reaching out (you read their article on roadmap prioritization)."
ChatGPT Result
Hi [Name],
I recently read your article on roadmap prioritization, and the framework you outlined completely changed how I think about feature tradeoffs.
I'm a junior PM at [Company], and I'm working on leveling up my prioritization skills. Your approach to balancing customer requests vs long-term vision really resonated with me.
Would you be open to a brief 20-minute coffee chat (virtual or in-person)? I'd love to learn more about how you approach these decisions in practice.
I know your time is valuable, so no worries if your schedule doesn't allow it. Either way, thanks for sharing your insights publicly.
Best,
[Your Name]
Grade: A – Respectful, specific, and genuine.
Claude Result
Hey [Name],
Your article on roadmap prioritization hit at exactly the right time for me—I've been wrestling with this exact problem at [Company].
I'm a junior PM trying to get better at balancing customer asks with long-term vision, and your framework made something click for me.
Any chance you'd be up for a quick 20-minute chat? I'd love to ask you a few questions about how you apply this in real-world scenarios.
Totally understand if you're swamped—just thought I'd ask.
Thanks for putting your work out there!
[Your Name]
Grade: A+ – Personal, warm, and genuine without being overly formal.
Gemini Result
Dear [Name],
I am writing to express my admiration for your recent article on roadmap prioritization. As a junior product manager, I found your insights particularly valuable.
I am currently seeking to develop my prioritization skills and would greatly appreciate the opportunity to speak with you regarding your approach to balancing competing priorities.
Would you be available for a brief 20-minute informational interview at your convenience?
Thank you for considering my request.
Sincerely,
[Your Name]
Grade: C – Way too formal. Sounds like a job application, not a networking email.
Winner for networking: Claude (most authentic and personable)
Head-to-Head Summary: Best AI for Email Writing
| Email Type | ChatGPT | Claude | Gemini |
|---|---|---|---|
| Cold outreach | A | ✅ Winner | C+ |
| Follow-up | A | ✅ Winner | D |
| Customer support | A | ✅ Winner | B |
| Internal team | ✅ Tie | ✅ Tie | B- |
| Networking | A | ✅ Winner | C |
Overall winner: Claude (best for natural, human-sounding emails)
The Tone Problem: Why Most AI Emails Fail
Here's what we learned: tone control is everything.
Even with identical prompts, Claude consistently produced warmer, more conversational emails because it's better at matching human tone.
But here's the problem: most people don't specify tone in their prompts.
Bad prompt:
"Write an email to a client."
Good prompt:
"Write an email to a client. Tone: friendly but professional."
Better prompt:
"Write an email to a client. Tone: warm and conversational, like you're talking to a colleague you respect but know well."
The Prompt Fixer solution: Choose from 7 tone presets:
- • Neutral
- • Direct
- • Friendly
- • Executive
- • Persuasive
- • Formal
- • Enthusiastic
Example:
- • Base prompt: "Write a follow-up email"
- • Add tone: Empathetic + Friendly
- • Result: An email that sounds human, not robotic
5 Email Prompt Templates You Can Use Today
Copy these A+ grade templates and customize for your needs:
Template 1: Cold Outreach
"Write a [word count]-word cold email to [audience] about [product/service]. Highlight one key benefit: [specific benefit]. Tone: [tone]. End with a CTA to [action]."
Template 2: Follow-Up
"Write a [word count]-word follow-up email to [recipient] who [previous action] but hasn't [desired action]. Tone: [tone]. Include [value add]. End with a low-pressure out."
Template 3: Customer Support
"Write a [word count]-word customer support email responding to [issue]. Company policy: [policy]. Tone: [tone]. Offer [solution]."
Template 4: Internal Update
"Write a [word count]-word email to your team updating them on [topic]. Key info: [details]. Tone: [tone]. Include next steps."
Template 5: Networking
"Write a [word count]-word networking email to [person] asking for [ask]. Mention [specific reason you're reaching out]. Tone: [tone]. Keep it respectful and brief."
FAQ
Which AI writes the most natural-sounding emails?
Claude, hands down. It's better at conversational tone and empathy than ChatGPT or Gemini.
Can I use ChatGPT for all my emails?
You can, but you'll get better results using Claude for customer-facing emails and ChatGPT for formal business communication.
How do I make AI emails sound less robotic?
Use The Prompt Fixer's tone controls (7 options) and specify style (professional, casual, etc.). Also, avoid generic openings like "I hope this email finds you well."
Does The Prompt Fixer work for email prompts specifically?
Yes. It optimizes any prompt, including email prompts. You can also use the LLM Recommender to find out which AI (ChatGPT, Claude, Gemini) is best for your specific email type.
Try It Free: Optimize Your Email Prompts
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