AI Email Assistant Comparison: Gemini Adds $0, Copilot $21, Superhuman $33

An AI email assistant costs $0, $21 or $33 a seat each month before you count the mailbox, depending on the product. Gemini in Gmail ships inside Google Workspace. Copilot Business adds $21 to Microsoft 365. Superhuman Business adds $33 to either one, and it also adds a second company to the path your email takes.

The short answer. For most teams, the best AI email assistant is the one already inside the mailbox you pay for. Start with Gemini in Gmail or Copilot in Outlook. Pay for Copilot only when you need triage and mailbox-grounded search. Buy Superhuman for a small group whose day is email, not for the whole company.

AI email assistant cost per seat, with the mailbox included

The list prices look like a three-way contest, and they are not. Gemini and Copilot sit inside the suite that hosts your mail. Superhuman's help centre says it supports only Google and Microsoft 365 hosted accounts, connected through their APIs. So it is always an addition to one of the other two bills.

That changes the sum. I modelled 25 seats, because 25 is the largest team Superhuman sells to without a sales conversation. Both Google and Microsoft Business Standard are $14 on an annual plan, so the mailbox cost cancels out of the comparison.

Working: (mailbox + AI) x 25 x 12. Larger firms face a different table. Microsoft 365 Copilot is $30 on a qualifying plan, and Superhuman Enterprise is priced by sales. Last verified 6 November 2026.

The $23.50 bundle is the number I would check before anything else. Set against a $14 Business Standard seat, it implies $9.50 for Copilot against $21 for the add-on. The page we read does not say how long that price lasts, so ask your reseller what it renews at.

The wider question of what a Copilot seat buys outside email is covered in the comparison of Copilot and Gemini across the whole suite. This post stays in the inbox, and it adds the third option that comparison leaves out.

AI email drafting is close to a commodity across all three

All three products will write you an email from a short prompt, and that is the least useful basis for choosing between them. Google lists Help me write and Suggested Replies for eligible Workspace plans. Microsoft's FAQ describes Draft with Copilot as generating full drafts from thread context and organisational information. Superhuman's AI page says Write with AI turns a few phrases into an email matching the voice of your sent mail.

The real difference is who starts the draft. Gemini and Copilot mostly wait for you to ask. Superhuman's pitch is the opposite. Its page describes waking up to an inbox where every email already has a draft reply, a feature it sells as Auto Drafts on the Business plan. That is a different product behaviour, not a better writing model, and it is the one drafting feature here worth paying for.

I would be careful about that benefit. A prewritten draft saves time only if the reader corrects it rather than sending it unread. None of the three vendors publishes a measured acceptance rate for its drafts on the pages we read, so you would be buying on the demo.

Tone and proofreading sit behind tiers. Copilot's coaching tips cover clarity, sentiment and tone, and Microsoft's overview lists them among in-app features for users without the add-on. Google's pricing grid marks Proofread from Business Standard upward, so Business Starter misses it. The practical gap for most teams here is small.

AI inbox triage is where the three products split apart

Triage is the job an email assistant is really hired for, and each vendor has limited it in a different way. Drafting saves minutes on messages you already chose to answer. Triage decides which messages get your attention at all, so an error costs more and the benefit is larger.

Copilot's triage needs the licence and looks forward only

Microsoft's Prioritize my inbox page says Copilot assigns high, normal or low priority as mail arrives, and gives a reason. It does not go back through older messages. It also skips mail outside the Inbox folder, meeting mail, and encrypted mail whose content it cannot see. The FAQ puts the feature behind a Copilot work licence and limits it to Tier 1 languages.

Gmail's AI Inbox is the widest offer with the narrowest reach

Google's help page lists AI Inbox for eligible Workspace plans, in English and in the US only. If your team sits in London or Bengaluru, take it off your comparison sheet for now. Conversation summaries and Help me write are global, so a non-US Gmail team still gets the assistant, but not the triage view.

Superhuman treats sorting as the product

Superhuman's Auto Labels separate marketing, cold pitches and social updates, and Auto Archive can remove them. That is filtering by category, not a ranking of what matters to you, though Custom Auto Labels on Business let you write rules in plain language. For a person receiving heavy inbound, I think this is the strongest practical argument for the product. It is also the easiest one to test in a week.

Email search with AI depends on what the assistant may read

Asking a question of your inbox only works if the assistant can read your whole mailbox, so search is where capability and data handling become the same decision. Each vendor answers that differently. Gmail offers AI Overviews in search on eligible Workspace plans. Superhuman's Ask AI searches inbox, calendar and the web, and sits on the Business plan.

Superhuman's help centre explains what makes that possible. With Ask AI enabled, your emails are stored through a SOC 2 compliant third-party vendor, encrypted in transit and at rest. That vendor is not named on the pages we could read. So the most useful Superhuman AI feature is also the one that creates the largest new copy of your mail.

Microsoft's position is the least clear of the three, and that is a problem of its own documentation. Its Outlook support page says unlicensed users can ask about inbox, calendar, meetings and other limited data. Its Copilot overview says Copilot Chat cannot use organisational data through Microsoft Graph. Those statements can both hold for a single open mailbox, but a buyer should not have to guess. Test it in your tenant before you tell staff what the free tier does.

Enterprise email AI controls favour the suite you already run

Admin controls are the clearest advantage of staying inside your suite, and they are also where plan tiers do the most damage. All three products reserve meaningful control for higher tiers. The tier that carries it differs, so check the plan you intend to buy rather than the vendor's best one.

Google's per-service switch is not on Business editions

Google's feature access page lists Enterprise and specific Education editions as supported for turning Gemini on or off by service. No Business edition appears. A separate smart features setting is named, but the page does not say which editions can use it. The Privacy Hub also describes audit logs covering Gmail, available through the Reporting API, and says client-side encryption restricts what Gemini can reach.

Microsoft has the deepest retention tooling

Copilot interactions have their own Purview retention location, separate from Teams chats, and they can be searched with eDiscovery. Sensitivity labels are honoured. There are limits too. Copilot in Outlook cannot read S/MIME or Double Key Encryption mail, and it does not work on group mailboxes or on mailboxes hosted outside Exchange Online.

Superhuman keeps SSO for Enterprise

The plan cards list Single Sign-On, advanced security and the Admin Console under Enterprise. The comparison table also has rows for SCIM and audit logs, whose per-plan values we could not read. So a 20-person firm that requires SSO may need a sales quote despite fitting inside the self-serve seat limit. Superhuman's Mail MCP documentation adds that MCP actions are not separately logged today.

Where each vendor sends message content and what it keeps

The data question is simpler than the vendor pages make it look, because the main variable is how many companies touch your mail. With Gemini or Copilot, your existing mail host also runs the assistant. With Superhuman, your mail host remains, and Superhuman and its AI vendors are added on top. None of this makes Superhuman unsafe. It does add parties to your review.

Superhuman's training language needs one direct question. Its help centre says plainly that neither it nor any vendor trains on your data. Its Mail page says never, unless consent is explicitly given. Its privacy policy says you can adjust a training control in account settings, and its suite plans table shows a model training row reading opt out, with off by default on the last tier. I read the suite table as covering lower tiers by column position, because the labels were not recoverable.

Those statements may be compatible, and I am not alleging a breach. But "consent" and "opt out" are different defaults. Ask which one applies to Mail on your plan, get the answer in writing, and put it in your contract using the data processing agreement clauses worth negotiating. Compare it too with how AI vendors rank on data retention. One useful point: organisation-managed accounts fall outside the privacy policy's coverage of content, so your own agreement governs.

Which AI email assistant fits which team

My recommendation is to default to the assistant inside your suite, then pay upward only for a named job. Very few 25-person firms should run a mailbox change or a second vendor review to get better summaries. Switching suites purely for an email assistant is a bad trade at any of these prices.

On Workspace. Use Gemini in Gmail. Your cost is already sunk. Accept that AI Inbox is US only and that per-service switches need an Enterprise edition, and confirm both limits suit you before you tell staff it is available.

On Microsoft 365. Start with Copilot Chat in Outlook. If your staff genuinely need triage and grounded search, price the $23.50 bundle before the add-on. Do not buy the licence for summaries alone, since Microsoft's overview lists draft and summary among in-app features without the add-on, subject to your tenant configuration.

For a handful of email-heavy people. Trial Superhuman with founders, sales leads or partners who live in their inbox. I think its case is speed and interface, with AI as a supporting feature. Do not roll it out company-wide. The 25-seat limit is a signal of who it is sold to, and individually adopted AI accounts create their own perimeter problem if the trial happens without IT.

Where this comparison is weakest

This post compares documents, not outcomes, and that is its largest gap. I did not run the three assistants on one mailbox, so nothing here says which one writes better or sorts more accurately. Treat the table as a guide to cost and terms. It is not a quality ranking.

Some sources were out of reach or partial

Superhuman's help centre blocked direct retrieval, so its retention wording comes from the indexed text of those pages, and the indexed copies were roughly six months old. The per-plan ticks on its feature table did not render. Google's pricing page served us Indian rupee prices, so its feature grid may differ by region. Google's $14 comes from its own US-priced AI page, while Microsoft's $14 comes from our earlier reading of its July 2026 list.

Superhuman has two price ladders

Superhuman also sells a suite with Pro and Business tiers that include Mail, Grammarly, Docs and Go. Its pricing page served rupees to us, so I have not converted it. The Mail plans page shows only annual dollars. Aggregators quote $30 and $40 for monthly billing, which fits the page's 17% annual discount, but I could not confirm that on Superhuman's own page. If you already pay for Grammarly seats, your comparison could look quite different from the table above.

The case against the suite default

The cost model ignores the value of time. If Auto Drafts and Auto Labels save a senior person even a modest amount each day, $33 a month is small against their salary. I have no independent measure of that saving, and vendors rarely publish one that survives scrutiny. So the $0 option wins on evidence available today, which is not the same as winning on outcomes.

Frequently asked questions

Where to start: two checks before you buy a seat

Open your admin console this week and find out what your staff already have. In Microsoft 365, check whether Copilot appears in Outlook for unlicensed users, and ask three of them to query their own inbox so you can see what the free tier really does. In Workspace, confirm your edition and test AI Overviews in Gmail search.

Then run one small trial, with one question attached. Give two email-heavy people a month of Superhuman or a Copilot licence, and ask them after 30 days which feature they would refuse to give up. If neither names one, you have your answer at $0 a seat, and your renewal conversation has a real number behind it.

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