A distribution list copies each message into every member’s personal mailbox, so replies leave the group and nothing is archived centrally. A shared mailbox keeps one copy that several people open, so the history stays in one place. In Microsoft 365 both exist as separate objects, along with a third one, the Microsoft 365 group. In Google Workspace there is no shared mailbox at all: the equivalent is a Google Group, optionally turned into a Collaborative Inbox. None of the four assigns an owner to a message, which is the part small teams actually struggle with.
Two tools that look identical from the outside
Your team needs one address customers can write to: contact@, info@, support@. Seen from the sender’s side, a distribution list and a shared mailbox are indistinguishable. The message goes to one address and, with luck, an answer comes back.
Inside the team, the two behave nothing alike. One copies each message to everyone; the other keeps a single copy that everyone opens. Small teams often pick whichever one somebody already knew how to set up, then live with the side effects for years. It is worth understanding what each tool actually does before the habits harden.
What a distribution list really does
A distribution list is a forwarding rule with a friendly name. Whether it is a Google Group used as a mailing list or a Microsoft 365 distribution group, the mechanism is the same: a message sent to the list address is copied into the personal mailbox of every member.
Microsoft is explicit about the intent. Distribution groups are for sending email notifications to a group of people, and Microsoft’s own guidance is that they fit best when you need to broadcast information to a set group of people, such as “People in Building A” or “Everyone at Contoso”. That is the design, not an oversight.
The copy-to-everyone mechanic has three consequences.
Replies leave the list. A customer writes to contact@, Sarah answers from her own mailbox, and the customer’s next message lands only there. The rest of the team has lost the thread. If Sarah is away for two weeks, the conversation is frozen in a mailbox nobody else can open.
There is less shared history than it looks. On a Microsoft 365 distribution group there is none at all: a colleague added to the list in September receives messages from September onward, and everything older sits scattered across personal mailboxes. A Google Group can keep past conversations online for new members to browse, but that archive only holds what went through the list address; the replies people sent from their own mailboxes never reached it. Either way, when the newcomer asks what was agreed with a supplier last spring, the honest answer is: nobody knows where that email lives.
And nobody owns anything. Every member received the same copy, so every member can assume someone else is dealing with it. Google concedes the point in its own product: Collaborative Inbox exists precisely to add ownership on top of a plain Google Group, with the ability to take a conversation, assign it to a member and mark it complete. If a bare list gave anyone ownership, that layer would have no reason to exist.
What a shared mailbox changes
A shared mailbox inverts the model: one mailbox, one copy of each message, several people allowed in. In Microsoft 365, this is the standard setup behind info@ and support@ addresses that a whole team watches, and Microsoft lists reception desks and front-desk mailboxes in the same breath.
Done properly, it fixes two real problems. History becomes central: everything sent to the address lands in one mailbox, and a newcomer can read last year’s exchanges on day one. One setting to know about: by default, Microsoft 365 saves replies sent as the shared mailbox to the sender’s own Sent Items folder, so an admin has to switch on the sent-items copy for the team’s replies to stay central too.
And there is no shared password. Every shared mailbox does have a matching user account, but its password is system-generated and, in Microsoft’s words, not known or intended for use. Microsoft’s instruction is to block sign-in on that account and keep it blocked. Each person gets in through their own account instead. We cover the setup in detail in our Microsoft 365 shared mailbox guide.
The trap is the improvised version. Plenty of small teams build a “shared mailbox” by opening an ordinary Gmail or Outlook account and passing the password around. Same phrase, very different object: that setup runs on a shared password, with the security exposure and provider lockouts that come with it, and it adds no structure at all.
Microsoft 365: three objects that look alike
This is where most of the confusion lives, because Microsoft 365 gives you three mail-enabled things that could all sit behind support@, and the admin center presents them side by side.
| Distribution group | Shared mailbox | Microsoft 365 group | |
|---|---|---|---|
| What happens to a message | Copied to every member’s mailbox | One copy in one mailbox | One copy in the group mailbox, plus optional copies for subscribers |
| Central archive of everything | No | Yes | Yes |
| Newcomer sees past messages | No | Yes | Yes |
| Shared calendar | No | Yes | Yes |
| People outside the company can be members | No | No, Microsoft is explicit that you cannot give a Gmail user access | Yes, if guest access is enabled |
| Send as the address | No | Yes, with permission | Yes, if enabled |
| Microsoft’s stated purpose | Broadcast to a set group | Several people need the same mailbox | Collaboration, including files and Planner |
Three details from Microsoft’s documentation matter more than the table itself.
The choice is close to irreversible. Microsoft states plainly that it is not possible to migrate a shared mailbox to a Microsoft 365 group. You can convert a user mailbox into a shared mailbox, but not a shared mailbox into a group. Picking wrong at the start means rebuilding later.
Deletion works differently than people expect. In a shared mailbox, you cannot prevent users from deleting messages, and Microsoft’s own advice when that matters is to create a Microsoft 365 group instead. In a group, someone who subscribed to receive conversations in their personal inbox can delete their copy without touching the group’s mailbox, and the reverse holds too.
A shared mailbox cannot encrypt what it sends. Because the mailbox has no security context of its own, no username and password in use, it cannot be assigned an encryption key. If members encrypt with their own keys, other members may not be able to read those messages.
The 25-user ceiling nobody mentions
Here is the limit that catches growing teams, and it is documented by Microsoft rather than inferred: a shared mailbox supports a maximum of 25 users. Beyond that, Microsoft warns that people accessing it at the same time might experience connection failures or duplicated messages, and recommends a Microsoft 365 group instead.
Read that again, because it is the whole problem in one sentence. Microsoft’s own answer to “too many people in one mailbox” includes the words duplicated messages. A shared mailbox does not coordinate anyone. It puts several people in front of the same list of emails and leaves them to work out who is doing what, and past a certain size the platform itself starts to struggle.
Storage has a ceiling too: 50 GB without a licence, 100 GB if you assign an Exchange Online Plan 2 licence. When it fills up, the mailbox keeps receiving for a while, then stops sending, then starts bouncing messages back to whoever wrote to you. On a support address that has been running for a few years with attachments, this is not theoretical. And each person who needs access must already have a licensed Exchange Online mailbox of their own; the shared mailbox itself is the only part that is free.
Google Workspace: there is no shared mailbox
If you are searching for “shared mailbox vs distribution list” with Google Workspace or G Suite in mind, the honest answer is that the comparison does not map. Google Workspace has no object called a shared mailbox in the Microsoft sense. You have three options, and they are not equivalent.
A plain Google Group. This is the distribution list. Messages go out to members, and if conversation history is on, the group keeps a browsable archive of what passed through the address. Replies sent from personal mailboxes still escape it.
A Google Group with Collaborative Inbox turned on. This is the closest thing to a team inbox that Google ships. Members can take a conversation, assign it to someone, and mark it complete, needing no further action, or a duplicate of another conversation. You can filter by “Assigned to me”, “Assigned to anyone” or “Not assigned”, and apply labels.
Two caveats before you count on it. Conversation history has to be enabled for Collaborative Inbox to work at all, and permissions decide who can do what: assigning and marking complete require the “Who can moderate metadata” permission, marking duplicates requires “Who can moderate content”. Owners and managers grant those. Also, marking a conversation as a duplicate locks it, and a resolved conversation that gets deleted cannot be restored.
Gmail delegation. Google itself points here when a team needs more than a Collaborative Inbox. A work or school account accepts up to 1,000 delegates, though Google notes that with typical use, 40 delegates can access a Gmail account at the same time; a personal @gmail.com account is capped at 10. A delegate can read, send and delete on your behalf, but cannot chat or change your password. One thing to know before you build a customer-facing address on it: when a delegate sends, their own email address appears. We went through the rest of the trade-offs in what Gmail delegation does well and where it stops, and compared the Google options in our Google Workspace guide for small teams.
The gap all of them share: ownership
Picture Monday morning at a three-person shop. A customer asked for a price on Friday evening. On a distribution list, all three got the copy, each assumed a colleague had it, and the customer heard nothing. Or two of them answer ten minutes apart, with two different prices. In a shared mailbox the failure is at least visible: the message sits there, marked read, belonging to no one.
So the interesting comparison is not really list versus mailbox. It is broadcast versus ownership. A distribution list gives you neither history nor ownership. A shared mailbox and a Microsoft 365 group give you history without ownership. A Collaborative Inbox gives you a thin layer of ownership, gated behind permissions, inside a product built for mailing lists.
Even a properly configured shared mailbox stops short of the essential thing: an owner per message. Five people can open the same mailbox, and the daily question stays unanswered. Who is handling this one? A message someone opened is not a message someone handled. There is no status, no internal note, no reliable way to mark a conversation done beyond folder rituals the team has to invent and police itself. That is exactly how two people end up replying to the same customer.
When a distribution list is the right choice
Credit where due: for one-way broadcast to a known group of people, a distribution list is exactly the right tool. Internal announcements to staff@ and automated alerts from a server are the obvious cases. So is a date change sent to thirty volunteers. It costs nothing and needs no training. If nobody is expected to reply, or replies can go to one person without follow-up, use a list and stop thinking about it.
The rule of thumb is the direction of the mail. Information flowing out: a list. Conversations flowing in: something with an owner per message.
When you need an owner per message
The moment customers, parents or members write back and expect an answer, you need what a list does not give and a shared mailbox only half gives. Each conversation needs one owner and a done state. It also needs a place for internal notes, so the team can discuss a message without forwarding it around.
That combination is what a shared inbox adds. With Trupeo, you connect the mailbox you already have, Gmail, Outlook, Microsoft 365 or any IMAP provider, and the team works on top of it: each person keeps their own login, each conversation gets one owner, an open or done status, notes and tags. The centralized history of a shared mailbox, plus the ownership none of the classic objects provide, without the 25-user ceiling.
A short decision guide to close:
- You only push information out: distribution list.
- Several people need to read one archive, replies are rare, and the team is small: shared mailbox or Microsoft 365 group.
- Several people answer every day and you need to know who owns what: shared inbox.
If you are starting from scratch, our complete shared inbox guide walks through the whole subject. To see what this looks like in practice, have a look at the features or our pricing.
Frequently asked questions
What is the difference between a shared mailbox and a distribution list?
A distribution list copies each incoming message into the personal mailbox of every member, so there is no central archive and replies sent by members never come back to the group. A shared mailbox stores one copy in one mailbox that several people open with their own credentials, so the history stays in one place and a newcomer can read past exchanges.
Should I use a distribution list or a shared mailbox in Office 365?
Use a distribution group when you are broadcasting information and nobody is expected to reply, which is the purpose Microsoft documents for it. Use a shared mailbox when several people need to read and answer the same incoming mail and you want one archive. Decide carefully: Microsoft states that a shared mailbox cannot be migrated to a Microsoft 365 group later.
How many people can use a Microsoft 365 shared mailbox?
Microsoft documents a maximum of 25 users. Past that, people using it at the same time might hit connection failures or duplicated messages, and Microsoft’s recommendation is to use a Microsoft 365 group instead.
Is there a shared mailbox in Google Workspace?
Not in the Microsoft sense. Google Workspace offers a Google Group, which behaves like a distribution list, a Google Group with Collaborative Inbox enabled, which adds assignment and a completed status, and Gmail delegation, which lets several people work inside one mailbox. Each covers part of what a Microsoft 365 shared mailbox does.
What is the difference between a shared mailbox and a Microsoft 365 group?
Both keep a central copy of the mail and a shared calendar. A Microsoft 365 group adds a collaboration workspace with files and Planner, can include people outside the company when guest access is enabled, and lets an admin restrict deletion. A shared mailbox is simpler and is the usual choice for a support or reception address inside one company.
Does a shared mailbox need a licence?
The shared mailbox itself does not, up to 50 GB of storage. Every person who accesses it needs their own licensed Exchange Online mailbox, and raising the shared mailbox to 100 GB requires an Exchange Online Plan 2 licence assigned to it.
Sources:
- Compare types of groups in Microsoft 365: the stated purpose of distribution groups as broadcast tools, the shared mailbox and Microsoft 365 group definitions, guest access, shared calendars, deletion behaviour for group subscribers, and the statement that a shared mailbox cannot be migrated to a Microsoft 365 group.
- About shared mailboxes in Microsoft 365: the 25-user maximum and the connection failures or duplicated messages warning, the 50 GB and 100 GB storage limits, the Exchange Online Plan 2 requirement, the system-generated password and the instruction to block sign-in, the inability to prevent deletions or to give access to external users, and the absence of an encryption key.
- Use a group as a Collaborative Inbox: the take, assign and mark-complete features, the assignment filters, the moderate metadata and moderate content permissions, and the locking of conversations marked as duplicates.
- Make a group a Collaborative Inbox: the requirement to enable conversation history first, who can turn the feature on, and Google’s own pointer to delegated accounts in Gmail for larger teams.
- Delegate and collaborate on email: the delegate limits of 10 for a personal account and 1,000 for a work or school account, the note that 40 delegates can access a mailbox at the same time with typical use, what a delegate can and cannot do, and the fact that the delegate’s own address appears when they send.
- Messages sent from a shared mailbox aren’t saved to the Sent Items folder: the default Sent Items behavior for replies sent as a shared mailbox, and the admin setting that keeps a copy in it.