I receive roughly 80 emails a day. Not newsletters (those go to a separate address). Real emails – clients, teammates, vendors, prospects. Before this experiment, I was spending 2-3 hours a day just on email. That’s 15 hours a week. That’s almost a part-time job. That’s unacceptable.
So I committed to a 30-day test of three AI-powered email clients: Superhuman, Shortwave, and Spark Mail. The rules were simple: each app gets 10 days as my exclusive email client. I sent and received over 1,000 emails total. By the end, I knew exactly which one I’d pay for – and which ones felt like AI hype with no substance.
The Short List
- Best for speed and power users: Superhuman – blazing fast, keyboard-driven, AI that actually saves time
- Best for Gmail power users who want a smarter inbox: Shortwave – excellent AI summarization and bundling
- Best for teams and cross-platform users: Spark Mail – best collaboration features, works everywhere
- Best free option: Spark Mail (generous free tier for individuals)
- The real email problem isn’t the client: It’s that you’re getting too many emails. None of these tools can fix that.
How I Tested
Each app was my exclusive email client for 10 consecutive business days. I connected my primary Gmail account (the one with 80+ daily emails) and used each app’s default settings with AI features enabled. No manual tweaking, no “I’ll customize it later.” Out of the box, as intended.
I tracked:
- Emails processed per hour
- Time to inbox zero each morning
- AI feature usage (how often I actually used the AI vs. ignoring it)
- Keyboard shortcuts learned and used
- Moments of frustration (“where is the damn button?”)
- Overall feeling at the end of each 10-day period
Superhuman: The Speed Demon That Costs Like One
Superhuman has a reputation – and a waiting list. The onboarding process involves a 30-minute video call with a real human who walks you through the features. It feels like buying a luxury car: someone explains every button and feature before you’re allowed to drive.
The core philosophy is simple: never touch your mouse. Every action has a keyboard shortcut, and they’re designed to be memorable. J and K move up and down (like Vim). E archives. R replies. Shift+R reminds you to follow up later. After three days, I was processing emails about 40% faster than in Gmail’s web interface.
The AI features are where things get interesting. Superhuman AI can write entire email replies based on context – it reads the incoming email, understands the thread history, and drafts a response in your voice. You can set a tone (professional, friendly, concise) and the AI adjusts accordingly. After a week of use, I was sending AI-drafted replies with only minor edits about 60% of the time.
The “Instant Reply” feature is borderline magic. For common email templates – “thanks, looking forward to it,” “let me check and get back to you,” “confirmed, see you there” – Superhuman generates the reply as you’re reading the email. One keystroke sends it. This alone saved me 20-30 minutes per day on repetitive responses.
Split inbox is another AI-powered feature that automatically categorizes emails into streams: Important, Newsletters, Cold Email, and everything else. The AI classification is surprisingly accurate after the first few days of training. I only had to manually re-categorize about 5 emails out of 800.
What Superhuman does well:
- Fastest email processing – keyboard shortcuts are brilliantly designed
- AI reply generation is the best of the three – context-aware and tone-appropriate
- Instant Reply handles routine responses without breaking flow
- Split Inbox categorization is accurate and learns over time
- Undo Send works reliably (up to 30 seconds after sending)
- Follow-up reminders are smart – they resurface emails when they need attention
- Snippets (templates) with AI-powered variable filling
- Read statuses show when recipients open your emails
Where Superhuman falls short:
- Price – $30/month is steep for an email client
- Gmail/Outlook only – if your company uses something else, you’re out of luck
- No free tier or trial without the onboarding call
- The onboarding call requirement feels pretentious (though it’s actually helpful)
- Mobile app is good but not great – the keyboard-driven design doesn’t translate well to phones
- Calendar integration is basic – no AI scheduling suggestions
- No team collaboration features – it’s strictly individual
- The AI can be too eager – I had to turn off auto-suggest for sensitive threads
Best for: Executives, founders, and anyone who processes 50+ emails daily and values speed above all else.
Shortwave: The Smart Gmail Layer
Shortwave is built on top of Gmail, which is both its biggest strength and its biggest limitation. It uses the Gmail API to create a smarter inbox on top of your existing email – no need to switch providers or change how you receive mail. If you’ve used Google Inbox (RIP), Shortwave feels like its spiritual successor.
The AI summarization is Shortwave’s headline feature. Long email threads are collapsed into AI-generated summaries at the top: “Alice asked about Q3 projections. Bob replied with updated numbers (+12% growth). Charlie needs the report by Friday.” Click to expand the full thread. This feature alone cut my email reading time by roughly 30% – instead of reading 15 messages in a thread, I read the AI summary and only expanded when I needed details.
Bundling is the other game-changer. Similar emails are grouped together: all shipping notifications in one bundle, all calendar invites in another, all newsletter digests in a third. You process bundles in bulk – archive all newsletters with one click. The AI decides what to bundle based on content patterns, and after a few days, the bundles were 95% accurate.
AI-powered search is genuinely better than Gmail’s native search. You can search in natural language – “show me the contract Dave sent last month” – and Shortwave finds the right email. It understands context, not just keywords. This is the only email client where I stopped dreading email searches.
What Shortwave does well:
- Best AI summarization – thread summaries are accurate and genuinely useful
- Bundling turns 80 individual emails into 15 digestible bundles
- AI search understands natural language and context
- Built on Gmail – no migration, no new email address
- Clean, modern interface that feels like a native app
- Free tier for individuals (with AI features included)
- Snooze is smarter – suggests snooze times based on email content
- Pin important emails to keep them visible regardless of date
Where Shortwave falls short:
- Gmail only – if you use Outlook, Fastmail, or anything else, you’re locked out
- Desktop app is Electron-based and uses significant RAM
- AI reply generation is behind Superhuman – less context-aware, fewer tone options
- No send-later scheduling built into the AI workflow
- Mobile app is iOS-only (Android users need to use the web app)
- Team features cost extra ($15/user/month for Business)
- The AI can sometimes over-summarize, missing important nuance in complex threads
- Bundle logic can’t be manually customized – you get the AI’s decisions
Best for: Gmail users who want a smarter inbox without changing their email address, and anyone drowning in long email threads.
Spark Mail: The Team Player
Spark Mail takes a fundamentally different approach: it’s built for collaboration. While Superhuman and Shortwave optimize individual email workflow, Spark adds shared inboxes, team commenting, and collaborative email drafting. If you run a small team handling a shared support@ or info@ inbox, Spark solves problems the other two don’t even address.
The AI features in Spark are more practical than flashy. The AI assistant can draft replies, summarize threads, and adjust tone – similar to Superhuman but with less polish. Instead of trying to be a ghostwriter, Spark’s AI focuses on making team workflows smoother: suggesting who should handle an email, flagging urgent messages, and automatically categorizing incoming mail.
The “Email Delegation” feature is genuinely useful for teams. An email comes into the shared inbox, Spark’s AI analyzes it, and suggests which team member should respond based on expertise and availability. One click assigns it. The assigned person sees it in their personal inbox with full context. No forwarding, no “did you see this?” Slack messages, no dropped balls.
Templates with AI variable filling work well for team consistency. Your support team can use the same templates with AI customizing the specifics – customer name, order number, issue details – while maintaining a consistent brand voice. This solves the “everyone responds differently” problem that plagues shared inboxes.
Cross-platform support is Spark’s superpower. Native apps for Mac, Windows, iOS, and Android – all with feature parity. If you switch between devices throughout the day (phone on the go, desktop at work, tablet on the couch), Spark is the only option that feels native everywhere.
What Spark Mail does well:
- Best team collaboration – shared inboxes, delegation, team comments
- Cross-platform with native apps on every major platform
- Generous free tier for individuals and small teams
- AI email categorization is fast and learns from team behavior
- Email templates with AI variable filling for consistent team responses
- “Gatekeeper” feature filters out low-priority email during focus time
- Integration with popular project management tools (Asana, Trello, Todoist)
- Snooze and send-later are reliable and easy to use
Where Spark Mail falls short:
- AI reply quality is behind Superhuman and Shortwave – more generic, less context-aware
- Thread summarization is basic compared to Shortwave
- Keyboard shortcuts exist but aren’t as comprehensive or intuitive as Superhuman’s
- The interface can feel cluttered – more options than you probably need
- AI features feel like add-ons rather than core to the experience
- Premium plan ($7.99/month) is needed for the best AI features
- Search is functional but not AI-enhanced like Shortwave
- Team features require everyone to use Spark – adoption can be a challenge
Best for: Small teams managing shared inboxes, and individuals who switch between multiple devices throughout the day.
Head-to-Head Comparison
| Feature | Superhuman | Shortwave | Spark Mail |
|---|---|---|---|
| Speed & Shortcuts | ????? | ????? | ????? |
| AI Reply Quality | ????? | ????? | ????? |
| Thread Summarization | ????? | ????? | ????? |
| Inbox Organization | ????? | ????? | ????? |
| Team Collaboration | ????? | ????? | ????? |
| Cross-Platform | ????? | ????? | ????? |
| Search | ????? | ????? | ????? |
| Price (Monthly) | $30 | Free-$15 | Free-$7.99 |
| Best For | Speed & Power | Smart Gmail | Teams & Multi-Device |
Where Each Tool Failed
Superhuman: The price is hard to justify for anyone who’s not processing 50+ emails daily. At $30/month, you’re paying $360/year for an email client. For that money, it should also make coffee. The mobile app also feels like an afterthought – on desktop, I was a productivity ninja. On my phone, I was squinting at tiny buttons and wishing for a touch-friendly interface.
Shortwave: The Gmail dependency is a dealbreaker for anyone not on Google Workspace. If your company switches from Gmail tomorrow, all your Shortwave workflows disappear. The desktop app also consumed more RAM than Chrome with 20 tabs open – on an older laptop, it was noticeably sluggish. And the AI summarization, while excellent, occasionally missed the one piece of information I actually needed from a thread.
Spark Mail: The AI features feel tacked on rather than deeply integrated. The reply suggestions are fine for “got it, thanks” but struggle with nuanced responses. I found myself ignoring the AI suggestions after the first few days and writing replies manually. For a tool that markets “AI-powered email,” the AI felt more like a checkbox feature than a core value proposition.
The Verdict
If you process 50+ emails daily and time is literally money: Superhuman is worth every dollar of that $30/month. After the 10-day test, going back to regular Gmail felt like swimming through molasses. The speed difference is real, and the AI reply generation saved me more time than the subscription cost. If your billable rate is over $50/hour, Superhuman pays for itself in a single afternoon.
If you use Gmail and want the smartest inbox without changing your workflow: Shortwave is the most intelligent upgrade. The thread summarization is genuinely useful (not gimmicky), and the bundling feature turned my chaotic inbox into something manageable. The free tier includes the AI features, so there’s no reason not to try it.
If you run a small team with a shared inbox: Spark Mail solves collaboration problems the other two ignore. The delegation and shared drafts features work well, and the cross-platform support means your team can use whatever devices they prefer. Just don’t expect the AI to write brilliant replies – that’s not where Spark shines.
My personal setup after this experiment: Superhuman for my work email (where speed matters), Shortwave for my personal Gmail (where AI summarization helps with long threads), and Spark for our team’s shared inbox (where collaboration is the priority). Yes, that’s three email clients. No, I don’t recommend this for sane people. But email is where I spend too much of my life, and these tools genuinely help.
The unspoken truth about email: The best AI email assistant can save you an hour a day. But it can’t save you from the meetings people schedule via email, the decisions that require actual thought, or the fact that some emails just need a human response. Use the AI for what it’s good at – and spend the time you save on work that actually matters.