Neither Microsoft nor Google offers a shared mailbox that spans both. Microsoft states plainly that you cannot give someone with a Gmail account access to a Microsoft 365 shared mailbox, and Gmail delegation requires a Google account on both ends. So a team with addresses on both sides needs a third-party tool, and the way that tool connects, browser extension, provider API or plain IMAP, decides more than the feature list does.
How a team ends up with mailboxes on both sides
It is more common than the marketing suggests, and it is rarely a decision anyone made.
A company runs on Microsoft 365 because that is what the accountant needed, but the old contact@ address still sits with the hosting provider from the first website, on IMAP. A school has staff on Microsoft 365 and a parents’ association with a Gmail address. A three-person firm merged with a two-person one and nobody has migrated anything. Somebody set up a Gmail account for the booking address years ago and it works, so it stayed.
None of these teams want to consolidate providers. Migrating an address means touching DNS, warning everyone who writes to it, and living with a month of forwarding. The question is not how to unify the mailboxes. It is how to answer them from one place.
The native tools stop at the ecosystem boundary
This is the part that surprises people, and both vendors document it.
Microsoft 365 shared mailboxes are internal only. Microsoft’s guidance is explicit: you cannot give people outside your business, such as people with a Gmail account, access to your shared mailbox. Its suggestion when you need that is to create a Microsoft 365 group instead. There are other constraints in the same page worth knowing: a shared mailbox supports a maximum of 25 users, and everyone who accesses it needs their own licensed Exchange Online mailbox.
Gmail delegation stays inside Google. A delegate opens the mailbox from their own Google account, which means they have to have one. A work or school account allows up to 1,000 delegates, though Google notes that with typical use, 40 can access a mailbox at the same time. Useful, and confined to one ecosystem. We went through the rest of its limits in what Gmail delegation does well and where it stops.
Forwarding is the usual improvisation, and it makes things worse. Point the Outlook address at the Gmail one and you now have copies in two places, replies going out from the wrong address, and no shared history. It is the pattern we described in shared mailbox vs distribution list, with an extra layer of confusion about which address the customer will see.
So the honest answer to “which native tool covers both” is: none of them. That is not an oversight, it is how the products are scoped.
Three ways a tool can connect, and what each costs you
Every shared inbox product picks one of these. It is the single most consequential thing about it, and it is usually buried in the documentation rather than on the pricing page.
Browser extension inside the webmail. The tool adds a layer on top of Gmail or Outlook on the web. Assignments and statuses appear inside the interface your team already knows, which makes adoption easy. The cost: you are tied to that webmail, in that browser. It generally will not work on mobile, and a tool built as a Gmail extension cannot cover an Outlook address at all, however much both vendors have in common. Gmelius is the clear example here: as observed in August 2026, it works with Gmail and Google Workspace, and does not support Outlook or Microsoft 365.
Provider API with OAuth. The tool connects to Gmail’s or Microsoft Graph’s API with a token you grant, and runs in its own interface. No password is shared, access is revoked in one click, and the tool can react to new mail in near real time. This is what serious cross-provider tools use for the big two. The cost: each provider has to be supported specifically, so the list of supported providers matters, and a provider outside the list is out of reach.
Plain IMAP. The oldest protocol, supported by essentially every mail host on earth. This is what covers the address at OVH, Gandi, Ionos, the regional host your predecessor chose in 2014. Slower to notice new mail than a push API, and worth checking how a given tool handles it, but it is the difference between a tool that covers your actual mailboxes and one that covers two of them.
The practical rule: a team on both Gmail and Outlook needs at minimum the second approach for both providers. A team that also has one legacy address somewhere needs the third as well.
“Works with Outlook” does not mean one thing
Worth pinning down before you trust a compatibility claim, because four different things are called Outlook.
- Microsoft 365 business accounts, the paid plans with your own domain. This is what most tools mean.
- Outlook.com or Hotmail personal accounts, free consumer accounts. Support here is genuinely inconsistent between products.
- Exchange on-premises, a server your organisation runs. Increasingly rare in small businesses, and rarely supported.
- An address that merely opens in the Outlook app but is hosted elsewhere, at your web host for example. This is an IMAP account with an Outlook client in front of it. Nothing about the Outlook app makes it a Microsoft mailbox.
That last one catches people out constantly. If your address is contact@yourcompany.fr sitting with your web host and you read it in Outlook, then a tool that “supports Microsoft 365” may not support your mailbox at all. What you need there is IMAP.
What to check before you commit
Six questions, in the order that matters. The first three eliminate most candidates.
- Does it support every provider you actually have, including the odd one? List your addresses first, then check, not the reverse.
- How does it connect, extension, API or IMAP? Ask directly if the site does not say.
- Do replies leave from the shared address, or from the individual’s own? This one has bitten teams after the fact, and it is exactly what Gmail delegation gets wrong: when a delegate sends, their own address appears.
- Does the whole team keep individual logins? If the answer involves a shared password, walk away; we covered why in sharing a mailbox without sharing the password.
- Does the price scale per user or per team? Cross-provider tools are almost all per seat, which is what makes a four-person team pay like a support department.
- What happens to your mail if you stop paying? The mail should live at your provider, with the tool as a layer on top, not the other way round.
Where the tools stand today
Verified on each vendor’s own pricing page in August 2026. Prices change; the connection model rarely does.
| Tool | Gmail | Outlook and Microsoft 365 | IMAP | Pricing as observed |
|---|---|---|---|---|
| Gmelius | Yes | No | No | From $19 per user per month, billed annually |
| Front | Yes | Yes, listed as Office 365 | Yes | Starter $25 per seat per month, annual, up to 10 seats |
| Missive | Yes | Yes | Yes | Starter $14 per user per month, up to 5 users |
| Trupeo | Yes | Yes | Yes | From 10 € per month excl. VAT, flat, not per user |
Missive is the broadest of the three on channels, since it also carries WhatsApp, Messenger, Instagram and SMS through Twilio. If your customers genuinely write to you on those, that is a real argument and we say so in our comparison. Front is built for larger support organisations and prices accordingly, with tiers at $65 and $105 per seat above Starter; our comparison goes through when that makes sense. Gmelius is a good tool if you are certain every address you will ever have is a Google one, which is the bet you are making; see our comparison.
What Trupeo does about it
Trupeo connects to Gmail, Google Workspace, Outlook, Microsoft 365 and any IMAP provider, through OAuth for the first four and standard IMAP credentials for the rest. You keep your addresses, all of them, wherever they are hosted. Each person on the team signs in with their own account.
Above those mailboxes, whichever provider they come from, the team gets the same thing: one owner per conversation, an open or done status, internal notes and tags, and a signal when a colleague is already replying. A message from the Microsoft 365 address and one from the old IMAP address sit in the same list and behave the same way.
The pricing is flat rather than per user, which is the other half of the problem for a small team: a shared inbox that costs the same at two people and at six. See our pricing and the features, or start with our complete shared inbox guide.
Frequently asked questions
Is there a shared inbox that works with both Gmail and Outlook?
Not from Microsoft or Google themselves. Microsoft states that a Microsoft 365 shared mailbox cannot be opened by someone with a Gmail account, and Gmail delegation requires a Google account on both sides. Covering both means a third-party tool that connects to each provider’s API, and several do, including Front, Missive and Trupeo as observed in August 2026.
Can I add a Gmail address to a Microsoft 365 shared mailbox?
No. Microsoft’s documentation is explicit that you cannot give people outside your business, such as people with a Gmail account, access to a shared mailbox, and suggests creating a Microsoft 365 group when external people need to be included.
Does a shared inbox tool need my email password?
It should not. Tools connecting to Gmail or Microsoft 365 use OAuth, where you grant a revocable token and never hand over a password. An IMAP address is different: it usually needs credentials, which is why an app-specific password is the right thing to use where the provider offers one.
What if one of our addresses is with a small hosting provider?
That is an IMAP mailbox, and IMAP support is the thing to check. A tool that lists only Gmail and Microsoft 365 will not reach it, even if you currently read that address in the Outlook app. Reading an address in Outlook does not make it a Microsoft mailbox.
Will my team have to change email address?
No, and any tool that requires it should be ruled out. A shared inbox connects on top of the mailboxes you already have. Your customers keep writing to the same addresses and keep receiving replies from them.
Sources:
- About shared mailboxes in Microsoft 365: the statement that you cannot give people outside your business, such as people with a Gmail account, access to a shared mailbox, the 25-user maximum, and the requirement for each user to have a licensed Exchange Online mailbox.
- Delegate and collaborate on email: the delegate limits for work and personal Google accounts, the note that 40 delegates can access a mailbox at the same time with typical use, and the fact that a delegate’s own address appears when they send.
- Gmelius pricing: observed in August 2026, Gmail and Google Workspace only with no Outlook or Microsoft 365 support, and plans starting at $19 per user per month billed annually.
- Front pricing: observed in August 2026, Office 365, Gmail, custom and IMAP as email options, with Starter at $25 per seat per month billed annually up to 10 seats, Professional at $65 and Enterprise at $105.
- Missive pricing: observed in August 2026, Gmail and Google Workspace, Outlook and Office 365 and IMAP, plus WhatsApp, Messenger, Instagram and SMS through Twilio, with Starter at $14 per user per month for up to 5 users.