Shared Mailbox Alternatives: What to Use When M365 Runs Out

Nobody searches for shared mailbox alternatives out of curiosity. Something broke: the mailbox filled up, a new hire could not be added, or two people answered the same customer and only found out when the customer replied twice.

Which of those happened decides your answer, and they have very different answers. This page is organized around that rather than around a list of products, because most of the lists you will find recommend the same $65-a-seat tool regardless of what actually went wrong.

Disclosure: we make InboxPilot, which appears below. It fixes exactly one of the five problems here and we say plainly which one.

Key takeaways

• Two people answering the same email: you need collision detection. That is a shared inbox tool, and free options do not have it.
• Mailbox full: the 50 GB cap lifts with an Exchange Online Plan 2 license. No new tool required.
• Cannot add more people: Microsoft documents a 25-user maximum. Past that you are changing tools, not settings.
• Too much email: no shared inbox reduces volume. It divides it. Different problem, different fix.
• Just need access for three people: stay free. Google and Microsoft both cover this at no cost.

The limits Microsoft actually documents

Most articles in this category assert that shared mailboxes "break at scale" without citing anything. Microsoft is more specific than that, in its own admin documentation:

"A shared mailbox supports a maximum of 25 users. If too many users access the mailbox at the same time, they might experience connection failures or duplicated messages." (Microsoft Learn, About shared mailboxes)

Duplicated messages means two agents answering one customer. That is the platform vendor naming the failure mode, which is more persuasive than a shared inbox vendor asserting it.

The other documented ceilings, all from the same page:

• 50 GB of storage without an Exchange Online Plan 2 license. On hitting it the mailbox stops sending, then stops receiving.
• No encryption. Mail sent from a shared mailbox cannot be encrypted, because the mailbox has no security context of its own.
• No way to stop users deleting messages. Anyone with access can remove mail permanently.
• No external access. A contractor on an outside domain cannot be granted access at all.

On the Google side the equivalent constraint is concurrency rather than headcount. Google's native shared inbox is built on Gmail delegation, which allows up to 1,000 delegates on paper but only around 40 accessing the account simultaneously under typical use, and Google notes that above-average use by one or more delegates can reduce that further. Browser extensions that poll Gmail are specifically named as a factor. (Google Workspace admin docs)

Which limit did you hit

The second row is worth pausing on. If storage is the only problem, buy the license and stop reading. Teams routinely migrate to a $65-per-seat product to solve a problem a storage license would have fixed.

Try the free options first

Two free paths cover the "several of us need to see support@" problem without any purchase, and one is new enough that most comparison articles have not caught up.

Google's native shared inbox. Workspace admins can create a shared email address directly from the Admin console under Users, and unlike the old Groups Collaborative Inbox it lives in real Gmail, including the mobile app. Included on Business Starter, Standard and Plus at no extra cost. (Google Workspace admin docs)

Hiver's free tier, which includes a shared inbox and runs inside Gmail, and Help Scout's free plan for five users, which adds a knowledge base.

What none of the free options give you is collision detection, automation, or reporting. They solve access. If access was the whole problem, you are done and you have spent nothing.

The paid shortlist

Ranked for teams that have confirmed a free option will not do.

1. InboxPilot

We publish this article, so weigh this accordingly. InboxPilot is on this list because of the last row of that table, not the first.

It is not a shared inbox. It is an AI layer that runs inside the Gmail or Outlook you already have, triaging and drafting replies grounded in your own documents so that repetitive mail is handled before a person opens it. It connects to a plain M365 or Google shared mailbox without a migration, which is unusual here.

Where it is the right answer: the volume is the problem. Your team is not colliding, they are buried.

Where it is the wrong answer, stated plainly: no assignment, no collision detection, no internal notes, no SLA reporting. If your trigger for reading this page was two people answering one customer, buy one of the three below instead.

Free covers 25 AI drafts on one inbox. Hobby is $29 a month for 200, Standard $149 for 1,500 with unlimited inboxes, Growth $249 for 4,000, Pro $499 for 12,000. Priced per workspace, not per seat. (inboxpilot.co/pricing)

2. Hiver

The lowest-friction upgrade for Google Workspace teams, because it runs as a sidebar inside Gmail rather than as a separate app. Assignment, collision detection, internal notes, SLA basics, and a genuine free tier.

Its two real drawbacks: the Gmail product does not support Outlook at all, and public reviews consistently report slowness under volume. Free, then $25, $55, and $85 per user per month.

3. Missive

The cheapest paid option at $14 per user per month, and the most even-handed about Gmail and Outlook, which matters if your team is split. Real-time collaborative drafting is its standout feature. The Starter tier caps at exactly five users, which catches teams out.

4. Front

The most complete coordination product in the category and the one with genuinely deep analytics. Worth knowing before you shortlist it: the advertised $25 Starter is capped at 10 seats, and the plan most teams need is Professional at $65 per seat per month.

If you are on Outlook, read Front's own documentation on Office 365 sync behavior before committing, because read-status sync carries conditions that confuse mixed teams. (Front help docs)

More detail: Front alternatives and Hiver vs Front.

What a shared mailbox is genuinely fine for

Worth saying, because the rest of this page is about its limits.

A plain shared mailbox is the correct choice for a team of two or three at low volume who need a shared address and nothing else. It is free, it is native in the client everyone already uses, and it requires no decision. Spending $1,500 a year to solve a coordination problem you do not have yet is the most common mistake in this category, and it is more common than outgrowing the mailbox.

The honest breaking point is not the 25-user cap. Almost nobody reaches it. It is the first time two people reply to the same customer and neither knows it happened, which can occur at four people on a busy address.

How to choose, in one paragraph

Name the specific thing that broke, because four of the five problems here have narrow fixes that do not involve changing tools at all: storage takes a license, encryption takes a real mailbox, external access takes a different user model, and headcount past 25 is the only one that genuinely forces the category change. If what broke was two people answering one customer, you want collision detection and the cheapest credible route to it is Hiver on Gmail at $25 or Missive on either platform at $14, with Front reserved for teams that need its analytics enough to defend $65 a seat. And if nothing broke except the volume, be careful, because every product in this category will happily sell you a better way to divide work you should not be doing by hand at all, which is the case we would make for InboxPilot and also the reason we send teams with a real collision problem elsewhere.

Related reading

• Best shared inbox email software: the full ranking of what replaces a shared mailbox.
• Best shared inbox for Outlook: the Microsoft 365 version of this decision, in more depth.
• Gmail shared inbox and shared mailbox tools: the Google side, including what Google calls each feature.
• Front alternatives and Hiver vs Front: if you have already shortlisted the paid tools.
• Shared mailbox auto-reply: the documented limits of native auto-replies on a shared address.

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Platform limits are quoted from Microsoft and Google's own administrator documentation and were re-checked in August 2026. Pricing comes from each vendor's own pricing page, checked August 2026, and is stated per user per month unless noted. Vendors change pricing frequently, so confirm current rates before purchasing. None of the vendors listed are affiliated with InboxPilot or have endorsed this article. InboxPilot is the publisher and is one of the tools discussed.