Shared mailboxes are one of the most useful things in Microsoft 365 — a single address like info@ or support@ that several people can read and reply from, without anyone juggling an extra password. They're also, quietly, one of the most common things to go slightly wrong. You grant someone access, and nothing appears. Or it shows up for a week and then vanishes after an update. Or it's there, but they can't actually send from it.
The reassuring news: it's almost always one of a small handful of causes, and none of them mean anything's broken. Here they are, roughly in the order worth checking.
First, what a shared mailbox actually is
A shared mailbox is a mailbox nobody logs into directly. Instead, people who already have their own account are given permission to open it alongside their own — so replies from support@ look like they came from the business, not from Jane's personal address. Because it works through permissions rather than a login, most of the hiccups come down to how and when those permissions take effect.
Cause 1: it just needs time
This is the big one. When you grant access, Outlook doesn't always pick it up immediately — the permission can take anywhere from a few minutes to a couple of hours to sync, and occasionally it only appears after Outlook is fully closed and reopened (or overnight). If you granted access a few minutes ago and it's not there yet, that's normal. Give it time before assuming something's wrong.
Cause 2: it needs adding manually
Microsoft 365 is supposed to add shared mailboxes automatically for anyone with access — a feature called auto-mapping. But if auto-mapping is off, or a recent update reset it, the mailbox won't appear on its own and has to be added by hand in Outlook's account settings. This is also the usual reason a mailbox 'disappears after an update' — the update changed how the account is configured, and it simply needs re-adding.
Cause 3: they can see it but can't send from it
Reading a shared mailbox and sending as it are two separate permissions, and it's completely normal to have one without the other. If replies hang on 'sending' and never leave, or come back with a permission error, the person has read access but not send-as permission — a quick, separate thing to switch on.
Cause 4: they're signed into the wrong account
Outlook can hold more than one account, and a shared mailbox only appears for the account that was actually granted access. If someone's looking at their personal profile, or a second work account they also use, the mailbox simply won't be there — not because anything's broken, but because they're looking in the wrong place. Confirming which account is signed in is a five-second check that saves a lot of head-scratching.
Cause 5: a guest can find the mail but not the shared files
A shared mailbox is just email. The files that live alongside a team — in Teams or SharePoint — are a separate permission, and it's common for someone (especially an outside guest) to have the mailbox but no link to the shared drive, or to see no button for it at all. If the complaint is 'I can see the emails but not the files,' that's the SharePoint or Teams side to grant, not the mailbox.
Full access, send-as, send-on-behalf: what the permissions mean
Almost every shared-mailbox quirk traces back to which of three permissions someone has. They sound similar but do different things:
| Permission | What it lets someone do | Typical use |
|---|---|---|
| Full access | Open and read the mailbox, manage its folders | Anyone who needs to work the inbox |
| Send as | Send so it looks purely from the shared address | A shared support@ or info@ front |
| Send on behalf | Send showing 'Jane on behalf of support@' | When you want the person named too |
The usual mix is Full access plus Send as, so replies simply look like they came from the business. Grant Full access on its own and someone can read but not send — which is the single most common 'it's not working' call we get.
The 'new Outlook' wrinkle
Microsoft has been rolling out a redesigned 'new Outlook,' and it handles shared mailboxes a little differently from the classic version — some setups that worked for years suddenly behave oddly after the switch. If a mailbox stopped working right after Outlook changed its look, that's a strong clue, and it's worth checking which version is in use before chasing other causes.
Shared mailbox, distribution list, or a real account?
A lot of confusion disappears once you match the tool to the job. A shared mailbox is for an address several people work together, like support@ or accounts@ — everyone sees the same inbox and the same sent items. A distribution list simply forwards a message on to a group's personal inboxes (handy for 'everyone@', but there's no shared record of who replied). And a full, licensed account is for an actual person. Reaching for a shared mailbox when you needed a distribution list — or the other way around — is behind a surprising number of 'why can't they see this?' puzzles.
- Shared mailbox — a team works one address together; keeps a common history; needs no extra licence
- Distribution list — one message fans out to a group's own inboxes; there's no shared, central copy
- Licensed account — belongs to a single person; it's the only one that truly 'logs in'
If you're setting a new one up, that choice is worth thirty seconds of thought — it saves the far longer conversation later about why the wrong people can, or can't, see something.
Quick reference: symptom to fix
| Symptom | Most likely cause | What to do |
|---|---|---|
| Nothing appears after granting access | Permission still syncing | Wait up to an hour; fully close and reopen Outlook |
| Was there, gone after an update | Auto-mapping reset | Add the mailbox manually in account settings |
| Can read it but can't send | No 'send-as' permission | Grant Send as (or Send on behalf) |
| Missing for one person only | Signed into the wrong account | Check which account is active in Outlook |
| Sees the mail but not the files | No Teams/SharePoint access | Grant access to the shared site, not the mailbox |
| Broke right after Outlook changed look | 'New Outlook' behaviour | Confirm the version; re-add or switch back |
If you've worked down this list and it still won't behave, it's usually a sign the permissions need setting properly from the admin side rather than in Outlook itself — a quick job for whoever manages your Microsoft 365.