How to automate a shared mailbox in Microsoft 365

You can automate a shared mailbox in Microsoft 365 in three stages. Start with free Outlook rules and categories to file and flag mail. Add Power Automate flows, included with most Microsoft 365 business plans, to save attachments and log enquiries. Then, when you need emails sorted by what they actually mean, routed to the right person and replies drafted for checking, add an AI inbox assistant.

First, get the shared mailbox basics right

Automation works better on a mailbox that’s set up properly. From Microsoft’s guidance:

• No licence needed up to 50 GB. A shared mailbox can hold up to 50 GB without its own licence. Going beyond that, or using archiving or litigation hold, needs an extra Exchange Online licence.
• Access is through people’s own accounts. Each person needs their own licensed mailbox, and you give them access to the shared one. Nobody should sign in to the shared mailbox directly; Microsoft recommends blocking sign-in for its account.
• Keep the group small. Microsoft says a shared mailbox supports up to 25 users. Beyond that, a Microsoft 365 group is the better tool.
• Anyone with access can delete messages. You can’t prevent it in a shared mailbox, which is one more reason to file things automatically.

Just as important: agree who checks the mailbox, how often, and what “dealt with” means.

Stage 1: Outlook rules and categories (free)

Open the shared mailbox in Outlook on the web (select your name, then “Open another mailbox”) or add it as an account in the new Outlook, and create rules there. Rules made this way run on Microsoft’s servers, so they work even when nobody has Outlook open. Some rules made in classic Outlook only run while Outlook is open on that computer.

Useful starting rules:

• move emails from known suppliers into an “Invoices” folder
• mark anything with “quote” or “enquiry” in the subject as important
• move newsletters and automated notifications out of the way

Many teams also use colour categories as a simple status system, such as “Sarah”, “Waiting on client” and “Done”, so everyone can see who’s dealing with what.

Stage 2: Power Automate flows (usually included)

Power Automate has a trigger called “When a new email arrives in a shared mailbox”. Outlook, SharePoint, Excel and Teams are all standard connectors, which Microsoft 365 business plans can use without an extra licence. Two flows most firms find useful:

Save attachments to SharePoint

1. Trigger on new emails with attachments in the shared mailbox.
2. For each attachment, create a file in a SharePoint folder, named with the date and sender so it can be found later.
3. Optionally move the email to a “Filed” folder.

Log every enquiry

1. Trigger on new emails to enquiries@ or info@.
2. Add a row to a SharePoint list or Excel table with the date, sender and subject.
3. Post a short message in a Teams channel so someone picks it up.

Three practical points from Microsoft’s documentation. The account running the flow needs full access to the shared mailbox, not just permission to send from it. Each flow watches one folder in one mailbox, so several mailboxes means several flows. And a flow that runs in the background is tied to the account that owns it, so use a dedicated account rather than one person’s login. If you’re weighing up other tools, see Power Automate vs Zapier vs Make.

Where rules and flows run out

Rules and flows follow fixed instructions: this sender, these words, has an attachment. Real email doesn’t always cooperate:

• a client replies to an old thread about something completely new
• a complaint arrives with the subject “Quick question”
• an invoice comes from a supplier your rules have never seen
• an urgent request looks exactly like a routine one

Rules can’t tell any of these apart, they can’t read what an attachment is, and they can’t write a sensible reply. Pile up enough of them and nobody knows which rule moved which email. Someone still has to read everything.

Copilot in Outlook doesn’t fill this gap either. It helps a person summarise, prioritise and draft when they ask, but it doesn’t sort, route and log a shared inbox for you.

Stage 3: an AI inbox assistant

This is the step that takes the reading off your team, and it’s what our inbox automation does. An AI inbox assistant reads each email as it arrives, including attachments, and:

• sorts it by meaning into the categories you choose: new enquiry, existing client, supplier invoice, complaint, spam or urgent
• routes it to the right person, team or system, with a one-line summary
• logs it, adding new enquiries to your CRM or a spreadsheet with the details filled in
• drafts a reply in your words, waiting in Outlook for someone to check, edit and send
• chases: anything unanswered after a set time is flagged to the person responsible, and complaints are flagged straight away

It works alongside the rules and flows you already have rather than replacing them.

Keep a person in the loop

An AI assistant will sometimes get things wrong, so design for that. Keeping a human in the loop means:

• replies are drafts by default, and a person sends them
• when the assistant isn’t sure what an email is, it passes it to a named person rather than guessing
• for the first few weeks, someone checks how it’s sorting and corrects it
• anyone can override it, easily

The data points

A shared mailbox is full of personal and confidential information, so any tool that reads it needs care:

• Use a business AI service with proper terms. We build with Anthropic’s Claude through its business service, which doesn’t train on customer data and is covered by a data processing agreement. We never use consumer chatbots with client data.
• Give it the least access it needs: the shared mailbox and the folders it files to, not everyone’s email.
• Decide what’s kept, and for how long, including any logs.
• Take extra care with sensitive email. Health or other highly sensitive information may need different handling. In-house AI on our own hardware in Cardiff is coming soon for work where data shouldn’t leave the building.

Not sure which stage you need? Our free automation audit looks at your shared mailboxes and tells you what’s worth automating. The inbox assistant is one of the standard automations included in Monthly AI Support.