Best Unified Inbox for Gmail and Outlook Together

Most "AI inbox" roundups quietly assume you live in one provider. That assumption breaks the moment you have a personal Gmail account on one side and a Microsoft 365 mailbox on the other — the shape of most freelancers, contractors, founders, and anyone whose day job and side work sit in different tenants. Half the popular AI email clients cannot open the Microsoft one at all.

This post is scoped narrowly on purpose. We are not asking which client has the best Gmail-only workflow, or the best Outlook-only workflow. We are asking which apps actually hold a Gmail account and a Microsoft mailbox in one inbox — with search that spans both, threading that does not double up when a Gmail user replies to a Microsoft user, and reply-from that picks the right account without you thinking. Getting those three right is the whole job.

The short answer#

For a genuine unified inbox across Gmail and Outlook, six apps qualify: AI Emaily, Missive, Spark, eM Client, Mailbird, and Superhuman Mail. All six connect to both providers, thread across accounts, search across accounts, and pick the correct sending account when you reply. Shortwave does not qualify — it is a Gmail-only client. Fyxer does not qualify either, but for a different reason: it is an overlay, not an inbox, and it lives inside each client separately rather than unifying them.

Our pick for most readers is AI Emaily, because the cross-provider case is the case we are actually built for and because the AI layer — triage, drafts, agent runs — inherits the unified view rather than being bolted onto Gmail-only plumbing. That said, if your job is a shared support queue that several people work at once across both providers, Missive has built harder on team collaboration than we have, and it is the better fit there. We build AI Emaily, and the honest scoping is the reason to keep reading rather than a footnote.

How we compared#

The comparison axis is deliberately not "which app has the most features." It is "which app holds a Gmail account and a Microsoft mailbox in one inbox without something small breaking." Five things carry almost all the weight, and every entry below is judged on them:

• Both providers in one inbox. The app connects Gmail and Microsoft 365 or Outlook.com natively (OAuth, not a per-tenant IMAP hack), and shows both accounts in a single all-inboxes view.
• Cross-account threading. A thread that starts with a Gmail sender and gets a Microsoft reply stays as one thread, not two — because threading in a real unified inbox has to work on Message-ID and In-Reply-To, not on the account the message lives in.
• Cross-account search. One search box, results ranked across both accounts, filters (from, has attachment, unread) that work regardless of which side the message is on.
• Correct reply-from. When you reply, the client defaults to the account the message was sent to, not to whichever account you had selected last. Getting this wrong is the classic cross-provider mistake and it leaks the wrong identity to the recipient.
• Parity of the little things. Snooze, archive, labels or folders, notifications, and offline all behave the same on both providers rather than working on Gmail and quietly not working on the Microsoft side.

We do not use pricing, ratings, or review counts as a comparison axis and we do not publish competitor prices. Prices change, plan names change (Grammarly acquired Superhuman in July 2025 and renamed the parent company Superhuman in October 2025, so "Superhuman" now names two different things), and a screenshot of a pricing page dated last quarter is a footgun. For every option below, check the current price on the vendor's own page before you decide.

We also do not fake tests. Everything below is judged on documented capability — what the vendor publishes about which providers they connect to, whether the account is added via OAuth, and how the client structures the inbox — plus first-hand use of the apps that connect to both providers on the same day.

Comparison at a glance#

Two rows in that table are worth reading twice. Shortwave and Fyxer both come up in every AI-email comparison, and both are excellent at what they do; neither is a candidate for a unified Gmail + Outlook inbox, and the reasons are different. Shortwave connects to Google Workspace only, so the Microsoft side of your life is not there at all. Fyxer connects to both providers, but as an overlay that sits inside your existing Gmail and your existing Outlook — the unification never happens because Fyxer is not the inbox.

The eight apps in detail#

The order below matches the table. AI Emaily first because it is the site you are reading and because we are built specifically for this case; everyone else in the order they earned. Sections that talk about our product name it plainly and disclose that we build it.

1. AI Emaily — AI-native inbox built for the cross-provider case#

AI Emaily connects to Gmail, Microsoft 365, Outlook.com, and any IMAP mailbox on the same account, and shows all of them in one all-inboxes view. Threading matches on Message-ID and In-Reply-To rather than on the account the message lives in, so a thread that starts on Gmail and continues on Microsoft stays as one thread. Search runs across every connected account with the same ranking; filters like from, has attachment, unread, and label do not care which side of the split the message is on.

The reason we lead on this specific post is that the AI layer sees the unified view too, not just one provider. Auto-triage, agent drafts, follow-up detection, and the Context Brain all operate across the whole inbox — the agent understands that a proposal you sent from your Gmail is being replied to from a client's Microsoft address, and treats it as one conversation. Every send in Copilot mode goes to you for approval first, Autopilot runs only inside the rules you set, and there is an undo and a full audit trail on every action.

Where we do not lead: we are not a shared team inbox in the way Missive is (see below), and if you want a classic PIM feel with local caches and no AI, eM Client is more mature there. Surfaces are downloadable macOS (Apple Silicon only) and Windows apps, iOS native, Android PWA, and any modern browser. There is no free plan — pricing is a 7-day free trial on Pro or Autopilot (card taken, $0 charged if you cancel before day seven); see [AI Emaily pricing](/pricing) for current numbers. We build AI Emaily.

2. Missive — the shared inbox that also happens to unify providers#

Missive's core product is a team inbox: multiple people assigned to the same conversation, internal comments alongside external replies, shared drafts, and rules that route work to the right person. That team layer sits on top of a proper multi-provider client — Missive connects to Gmail, Microsoft, and generic IMAP accounts, threads across them, and searches across them.

For an individual who happens to have Gmail and Outlook, Missive is more app than they need — the collaboration surface takes up real estate that a solo user gets no value from. For a support desk, an operations team, or a two-to-five person business whose shared queue lives across both providers, Missive is genuinely the better fit than we are. Available on macOS, Windows, Linux, iOS, Android, and web. Packaging is per-user with a free tier for small teams and paid tiers above it; check the current numbers on Missive's own pricing page.

3. Spark (Readdle) — the native-feeling multi-account inbox#

Spark connects to Gmail, Microsoft 365, Outlook.com, iCloud, Yahoo, and IMAP, and has done for years. Its Smart Inbox groups messages by type (personal, newsletter, notification) across all connected accounts, threading and search work across the whole set, and reply-from defaults to the correct account. On macOS and iOS it feels native in a way most cross-platform clients do not.

Spark added an AI drafting layer more recently, but the reason it is on this list is the underlying multi-account inbox rather than the AI. If you want a client that will hold a Gmail and a Microsoft mailbox side by side and get out of your way, Spark is a solid pick. Available on macOS, iOS, iPadOS, Android, and Windows. Packaging is a free tier plus paid Premium and team plans; verify the current split on Readdle's site.

4. Superhuman Mail — fast keyboard triage across both providers#

Superhuman Mail connects to Gmail and Microsoft 365, and the whole product is oriented around a keyboard-first triage loop: open, decide, hit a key, move on. The unified inbox holds both providers, search and threading span accounts, and split inbox views can separate work and personal without hiding either.

One naming caveat: Grammarly acquired Superhuman in July 2025 and renamed the parent company Superhuman in October 2025, so "Superhuman" now points at two different things — Superhuman Mail (the client) and the Superhuman Suite (Grammarly's productivity bundle). This post is about Superhuman Mail. Available on macOS, Windows, iOS, Android, and web. Packaging is per-seat monthly or annual across Starter, Business, and Enterprise tiers; check the vendor page for current pricing.

5. eM Client — the mature multi-account desktop PIM#

eM Client is the traditional-desktop-client answer. It connects to Gmail, Microsoft 365, Outlook.com, Exchange, IMAP, and calendar and contacts alongside mail. Everything is local, the multi-account view is real, cross-account search and threading work, and features like PGP, side-by-side calendar, and per-account signatures are there without an add-on.

There is a light AI layer for compose and translate, but the reason to pick eM Client is the maturity of the client itself. If you want the feel of a desktop PIM that opens both a Gmail and a Microsoft account and treats them as first-class citizens without inventing a new metaphor, eM Client is where it lives. Available on Windows, macOS, iOS, and Android. Packaging is a free tier for personal use, a one-time Pro license, or a subscription; check the current split on the eM Client site.

6. Mailbird — the Windows-first multi-account client#

Mailbird is the Windows equivalent of the pick above. It connects to Gmail, Microsoft 365, Outlook.com, IMAP, and Exchange, holds them in a unified inbox with cross-account search and threading, and layers third-party app integrations (Slack, WhatsApp, Asana) alongside email rather than trying to become each of them.

A macOS build exists but Mailbird's home is Windows, and Windows users who want a mature multi-account client with room to grow are the natural audience. AI features have been added recently but are not the reason to be here. Packaging is a subscription for Personal or Business tiers, plus a lifetime option that appears and disappears from the site periodically; check the vendor page for the current shape.

7. Shortwave — great, and Gmail-only#

Shortwave is one of the best AI-native email clients shipping, built by former Google engineers with strong semantic search and a fast triage loop. It is on this list because it is the app most readers of this post will already be thinking about, and it is important to be clear about the constraint: Shortwave connects to Google Workspace only. There is no Microsoft 365 connector, no Outlook.com connector, and no generic IMAP.

For a Gmail-only workflow, Shortwave has built harder on Gmail archive search and thread summarisation than we have, and it is a legitimate pick for that reader. For anyone with a Microsoft mailbox on the other side of their day, Shortwave cannot open it. That is not a criticism — it is a scope decision the vendor has made — but it disqualifies Shortwave from the specific question this post is answering. Packaging is a free tier plus paid tiers on shortwave.com; verify at write time.

8. Fyxer — an overlay, not an inbox#

Fyxer is an AI layer that plugs into Gmail and Microsoft 365 and does triage, categorisation, drafts, and meeting notes inside the client you already have. It works well at what it does, and the fact that it supports both providers is why it comes up in searches for a unified Gmail + Outlook experience.

But Fyxer is not a client. It sits inside Gmail's web interface and inside Outlook, and the unification never happens because there is no third surface to unify into — you still open Gmail to see Gmail, and Outlook to see Outlook, with Fyxer working inside each. That is a genuinely useful shape for someone who is happy in their current client and only wants AI added; it is not a unified inbox in the sense this post is asking about. Packaging is per-user with a trial; check the current tiers on fyxer.com.

How to choose for your situation#

The right pick is a function of who is going to use it and what the other side of your workflow is. Four common shapes, and the honest recommendation for each.

1. 1

   You are one person with a personal Gmail and a work Microsoft mailbox

   AI Emaily is the intended reader of this post: unified inbox across both, AI triage and drafts that see the whole thing, approve-before-send by default. Spark is the strong non-AI alternative if you want a native-feeling client and are happy to run triage manually.

2. 2

   You are a small team sharing a support or ops queue across both providers

   Missive is the better fit. The collaboration surface is what it is built for — assignments, internal comments, shared drafts across a queue that spans Gmail and Microsoft. AI Emaily does have shared inbox and delegation, but Missive is more mature there and it is the honest recommendation for a real shared-queue team.

3. 3

   You want a mature classic desktop client, no AI required

   eM Client on Windows or macOS, Mailbird on Windows. Both hold Gmail and Microsoft accounts as first-class citizens with local caches, calendar and contacts, and the traditional PIM shape. Pick eM Client for the cleaner cross-platform story; Mailbird if you are Windows-first and want the app integrations.

4. 4

   You are Gmail-only or Outlook-only and this post found you by accident

   If you are Gmail-only, Shortwave is a strong pick and this post is not the right one to read next — try our guide to the best email client for Gmail. If you are Microsoft-only, our guide to the best email client for Microsoft 365 is more useful than any of the cross-provider clients here.

One last honest note on ranking. AI Emaily leads the table because the cross-provider case is what we are built for and because this is our site. It does not lead every table on the internet, and it should not — Shortwave is the better Gmail-only pick, Missive is the better team-queue pick, eM Client and Mailbird are more mature classic clients. Getting those four calls right is the reason to take the rest of the recommendation seriously.