Inbox Zero
Open-source AI email assistant for Gmail and Outlook that triages your inbox and pre-drafts replies you still send yourself
Inbox Zero is an open-source AI email assistant you can self-host: it connects to an existing Gmail or Outlook account, sorts mail by rules you write in plain English, and pre-drafts replies in your own tone that you still choose to send. It had 12,154 GitHub stars as of 5 September 2026 and takes functional commits most days. The part a founder should read before deploying it is not the feature list but the licence — AGPL-3.0 with two extra terms, one of which requires a paid enterprise licence once five or more people in your organisation use it for work.
What Inbox Zero is
Inbox Zero (github.com/elie222/inbox-zero) is a TypeScript application from Inbox Zero Inc. that sits on top of a mail account you already have rather than replacing it. You keep your address and your provider; it adds a layer that triages, drafts and reports. The repository was created in July 2023 and is under continuous development — the default branch took ordinary product commits on most working days through 4 September 2026, and there were 196 open issues at capture. Docker images are built from every push to the main branch, and tagged releases are cut for its desktop client.
- Rules written in plain English. Rather than assembling filter conditions, you describe how a category of mail should be handled and the assistant applies that description to incoming messages.
- Replies arrive pre-drafted, not pre-sent. It writes a reply in your tone and leaves it as a draft. The decision to send stays with you, which is the distinction that makes the whole thing safe to try on a real account.
- Reply Zero tracks two queues. Mail you owe a reply to, and mail you are waiting on. Those are the two lists a founder normally keeps badly in their head, and the second one is where deals quietly stall.
- Bulk unsubscribe and bulk archive. One-click unsubscribe from senders you never open, plus bulk archiving to clear a backlog you are never going to read.
- A cold email blocker. Automatic blocking of unsolicited outreach. Worth noting if you also send cold email, because the people you are prospecting increasingly run something like this too.
- It is drivable from Slack and Telegram. You can act on the inbox from a chat tool that is already open, alongside meeting briefs assembled from mail and calendar, and attachment filing to Google Drive or OneDrive.
Read the licence before you deploy it, not after
The repository carries the GNU Affero General Public License v3.0 plus a short block of additional terms, and it is the additional terms that decide whether you may use it. This is what open core looks like from the licence side rather than the feature side, and it is stated plainly enough that you can settle the question in a minute — which is more than can be said for most projects with a commercial parent.
- Under five business users, you are exempt. The LICENSE file exempts personal use, educational use, research, and organisations with fewer than five business users. A solo founder or a three-person team can self-host it and owe nothing.
- At five, you need an enterprise licence. The stated threshold counts employees, contractors and users who use it for business purposes. This is the line a growing team crosses without anyone noticing, so it is worth writing down next to your headcount plan rather than discovering later.
- You may not sell it or resell access to it. A commercial monetisation restriction bars selling access, offering it as a paid service, or folding it into a product you license for profit, absent written permission from the company.
- The AGPL underneath still binds. If you modify it and let other people use your modified copy over a network, the AGPL's source-sharing obligation applies as normal. The extra terms narrow what you may do; they do not loosen the base licence.
- There is a hosted version. The maintainers run a paid hosted service, which is the route that removes the licence question entirely. Self-hosting is a real option here, not a token one, but it is not the only one.
Why an inbox tool belongs in a growth stack at all
It is easy to file this under personal productivity and stop thinking about it. For a founder that is a mistake, because three growth motions all terminate in the same inbox: replies to cold outreach, enquiries from your website, and every conversation in founder-led sales. The cost of a cluttered inbox is not stress. It is a reply that arrived and never got answered, which looks identical from the outside to a prospect who was never interested.
- Response time is a variable a small team can actually win. You will not out-spend a funded competitor, and you may not out-build one. Answering the same day is available to you and often is not available to them.
- The awaiting-reply queue is a pipeline in disguise. Every deal that dies of silence dies in that list. Making it visible is most of the fix, whichever tool renders it.
- What you unsubscribe from is data. A month of one-click unsubscribes is an honest inventory of the newsletters, tools and vendors that earned nothing from you — useful if you are about to start a newsletter yourself.
- Email is still the channel people answer. We send our own customers a daily brief by email and let them reply to it directly; those replies arrive as ordinary mail and reach their growth officer. Attention lives in the inbox even for people who spend all day in a chat app.
The part we would keep a person on
We run the same draft-then-approve shape on the outbound side, so the caution worth passing on comes from our own logs rather than from anyone's README. Automated actions rarely fail loudly. Ours recorded a clean success while the thing itself had not happened, and we only found it because we later built a readback that compares what was proposed against what actually landed. An inbox has exactly the same blind spot, and it is worse there, because the evidence of a mistake is a message that is no longer in front of you.
- Keep the destructive actions reviewable. Archive, block and unsubscribe are the ones you will never notice went wrong. Give them a week of spot checks before you trust them, and keep an undo path.
- A draft is the right default for a reply. Drafting is cheap to correct and sending is not, so leaving the send with a person is human-in-the-loop doing real work rather than ceremony.
- Start with one rule, not the whole inbox. Pick the category you are most confident about — receipts, or newsletters — and let it run alone until the handling is boring.
- Watch what a rule does to strangers. A cold email blocker cannot tell an unwanted pitch from a first message by a customer who found you. That is the one class of error that costs revenue rather than time.
FAQ
- Is Inbox Zero free to self-host?
- For personal use, education, research, or an organisation with fewer than five business users, yes — the LICENSE file exempts all four. At five or more employees, contractors or users using it for business purposes, the additional terms require an enterprise licence from the company. The AGPL-3.0 base licence also still applies, so a modified copy offered to others over a network carries the usual source-sharing obligation.
- Does Inbox Zero work with Outlook or only Gmail?
- Both. The README documents OAuth setup for Google and Microsoft, and the project ships local emulators for each so you can develop against them without touching a real mailbox. If you are on a provider other than those two, this is not your tool.
- Does it send email on my behalf?
- Its replies are written as drafts, and the send stays a human decision. That is the design choice worth keeping whatever you use: an assistant that drafts is easy to correct, and one that sends is only as good as its worst day. The same reasoning is why we gate outbound behind an approval step on our own product.
- How is this different from a shared inbox or a help desk?
- A help desk such as Chatwoot or LibreDesk is built for a team answering strangers, with assignment, queues and SLAs. Inbox Zero is built for one person's own mailbox, where the problem is not routing but volume and the reply you forgot. If several people answer the same address, you want the help desk.
You built it. Now grow it.
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