Unified Inbox That Works With Gmail and Outlook Together

If you want a unified inbox for Gmail and Outlook accounts without alt-tabbing between two apps, the question narrows fast. Most "AI email" roundups quietly assume you live in Gmail. The moment a personal Gmail sits on one side of your day and a Microsoft 365 mailbox sits on the other — the shape of most contractors, freelancers, founders, and anyone whose day job and side work are in different tenants — half the popular clients cannot open the Microsoft one at all.

This roundup is scoped narrowly on purpose. We are not asking which client has the best Gmail-only workflow. We are asking which apps actually merge a Gmail account and a Microsoft mailbox into one view — with search that spans both, threading that does not split when someone replies from the other side, and reply-from that picks the right identity by default. Six clients pass; two commonly-cited alternatives do not, for two very different reasons.

The short answer#

For a genuine cross-provider unified inbox that shows Gmail and Outlook together in one view, six apps qualify in 2026: AI Emaily, Missive, Spark, Superhuman Mail, eM Client, and Mailbird. Each connects to both providers via OAuth, threads across accounts, searches across accounts, and defaults reply-from to the account the message was sent to. There is no per-tenant IMAP workaround required, and none of them ask you to switch between two windows.

Our pick for most readers is AI Emaily, because the cross-provider case is the case we are built for and because the AI layer — triage, drafts, autonomous follow-ups — sees the merged view rather than sitting on top of a Gmail-only stack. That said, if what you actually need is a shared queue two or more people work together across both providers, Missive has built harder on real-time collaboration than we have, and it is the better fit there. We build AI Emaily; the honest scoping is why the rest of this page is worth reading.

How we compared#

The axis is deliberately not "which app has the most features." It is "which app holds a Gmail and a Microsoft mailbox in one place without something small breaking." Five things carry the weight, and every option below is scored on them:

• Native connection to both providers. Gmail and Microsoft 365 (or Outlook.com) added via OAuth, not a per-tenant IMAP fallback. IMAP works for Microsoft consumer accounts but is a second-class citizen on Microsoft 365 tenants where an admin has disabled it — verify on Microsoft's own IMAP/POP settings page before assuming it will hold.
• One inbox, one keystroke to enter it. A single all-inboxes view that shows both providers ranked together, without a tab switch or an account dropdown to get there.
• Cross-account threading. Messages thread by Message-ID and In-Reply-To (per RFC 3501), so a conversation that starts on Gmail and gets a Microsoft reply stays as one thread rather than splitting into two.
• Cross-account search. One search box, results merged and ranked across every connected account, filters (from, has attachment, unread, label/folder) that work regardless of which side the message lives on.
• Correct reply-from. When you reply, the client defaults to the account the message was addressed to — not to whichever account was highlighted in the sidebar last. Getting this wrong quietly leaks the identity split you were trying to keep clean.

We do not publish competitor prices or ratings. Pricing tiers, plan names, and free-tier rules change without notice — and Superhuman in particular now points at two different products since Grammarly acquired the email client in July 2025 and renamed the parent company Superhuman in October 2025. For every option below, check the current packaging on the vendor's own page before you commit. Where a packaging shape is worth calling out, we describe the shape (free tier, trial, per-seat, one-time) rather than the number.

We also do not fake tests. Everything below is judged on documented capability — what the vendor publishes about which providers they connect to, how the inbox is structured, and what the AI layer actually operates on — plus first-hand use of the apps that qualify.

Comparison at a glance#

Two rows are worth reading twice. Shortwave and Fyxer both appear in almost every AI-email comparison, and both are good at what they do. Neither is a candidate for a unified Gmail + Outlook inbox, for two different reasons. Shortwave is a Google Workspace client — the Microsoft side of your life is not there at all. Fyxer connects to both providers, but as an overlay that runs inside each existing client. The unification never happens because Fyxer is not the inbox.

The tools#

The order matches the table. AI Emaily first because the cross-provider case is what we are built for and because this is our site; the rest in the order they earned. Sections that discuss our product disclose that we build it.

1. AI Emaily — AI-native inbox built for the two-provider reader#

AI Emaily connects to Gmail, Microsoft 365, Outlook.com, and any IMAP mailbox on the same account, and shows every account in a single all-inboxes view. Threading matches on Message-ID and In-Reply-To rather than on which account the message lives in, so a conversation that starts on Gmail and gets a Microsoft reply stays as one thread. Search is one box, ranked across every account, with filters (from, has attachment, unread, label, folder) that ignore the account boundary. Reply-from defaults to the account the incoming message was addressed to, so the identity split you set up on day one stays clean.

What makes us the pick for this specific reader is that the AI layer sees the merged inbox, not one provider. Auto-triage, agent drafts, follow-up detection, and the Context Brain all operate across the whole thing — the agent recognises 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 only runs inside rules you set, and there is an undo plus a full audit trail on every action. The Context Brain is user-set rather than trained on your past mail.

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

2. Missive — the shared inbox that also unifies 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 collaboration layer sits on top of a real multi-provider client — Missive connects to Gmail, Microsoft, and generic IMAP, threads across all of them, and searches across all of them.

For a solo user Missive is more app than they need; the collaboration surface takes up screen real estate a single operator gets no value from. For a support desk, an operations team, or a two-to-five-person business whose shared queue spans 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; verify current shape on Missive's pricing page.

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

Spark has held Gmail, Microsoft 365, Outlook.com, iCloud, Yahoo, and IMAP accounts side by side for years. Its Smart Inbox groups messages by type — personal, newsletter, notification — across every connected account, 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 manage.

Spark added an AI compose layer more recently, but the reason it earns a spot here is the underlying multi-account inbox rather than the AI. If you want a client that holds a Gmail and a Microsoft mailbox side by side and gets out of the 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 — keyboard-first 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. If your day is high-volume email and you already touch-type shortcuts, Superhuman's speed is real.

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 (the Grammarly-owned productivity bundle). This entry 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 current numbers on the vendor page.

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

eM Client is the answer for readers who want the traditional-desktop-client feel. It connects to Gmail, Microsoft 365, Outlook.com, Exchange, IMAP, and holds calendar and contacts alongside mail. Everything is local, the multi-account view is real, cross-account search and threading work, and features like PGP encryption, 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 mature PIM that opens 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; verify 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 replace them.

A macOS build exists, but Mailbird's home is Windows, and Windows users who want a mature multi-account client with app integrations 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 strongest AI-native email clients shipping — built by former Google engineers, with semantic search across the Gmail archive that is genuinely ahead of most of the field. It appears in this table because it is the app most readers of this post will already be thinking about, and because it is important to be plain about the constraint: Shortwave connects to Google Workspace accounts 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 paid subscription with a trial; verify current tiers on shortwave.com 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 keeps coming up in searches for a unified Gmail + Outlook experience.

But Fyxer is not a client. It runs 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 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 answering. 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

   One person with a personal Gmail and a work Microsoft mailbox

   AI Emaily is the intended reader of this post: one 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

   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 has 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 Microsoft-only and landed here by accident

   If you are Gmail-only, Shortwave is a strong pick and this post is not the right next one — try our guide to the best email client for Gmail. If you are Microsoft-only, a client oriented at Microsoft 365 will treat you better than any cross-provider option on this page.

One honest note on the ranking. AI Emaily leads the table because the cross-provider case is what we are built for and because this is our site — the reader is on aiemaily.com and we are entry #1 by design. That does not mean we lead every table on the internet, and we 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 seriously.