Exchange mailboxes

On-premises Exchange

This page covers hosted on-premises Exchange. For Microsoft 365 mail see Exchange Online mailboxes — the screens are different.

Exchange > Mailboxes lists the mailboxes in the organization. It is the screen you spend most of your Exchange time on.

Creating a mailbox

1. Open Exchange > Mailboxes and choose Create Mailbox.
2. Select the user the mailbox belongs to, or create one as part of the process.
3. Set the email address — the local part, and the domain from those allocated to the organization. If the domain you want is missing, allocate it first under organization domains.
4. Choose a mailbox plan. This decides the mailbox’s size limits and which features it gets. See mailbox plans.
5. Save.

You are consuming a quota

Each mailbox counts against the organization’s mailbox quota. When the quota is exhausted, creation fails — check the counter on the list page before starting a bulk onboarding rather than discovering the limit halfway through.

The mailbox settings tabs

Opening a mailbox gives a set of tabs. Each covers a distinct area, and they save independently.

Tab	What it controls
Mailbox Settings	The mailbox’s general properties and its plan
Addresses	Every email address the mailbox accepts, and which is primary
Mail Flow	Forwarding and delivery options
Permissions	Who else can access this mailbox, and how
Advanced	Storage limits and lower-level Exchange attributes
Member Of	Distribution lists the mailbox belongs to
Out Of Office	Automatic replies
Mobile	Devices synchronizing with this mailbox
Rules	Server-side rules that act on the mailbox’s mail
Setup	Client configuration details for the end user

Addresses

A mailbox can hold several addresses; one is the primary, which is what outbound mail is sent from. The others are accepted for delivery.

Changing the primary address changes what recipients see

Existing mail still arrives at the old address as long as it remains in the list, but everything the user sends afterwards comes from the new one. Tell the user before you change it — the first they otherwise know is a colleague asking who the message is from.

Permissions

Three kinds of access, and the difference matters:

• Full access — open the mailbox and read its contents. It does not by itself allow sending.
• Send As — send mail that appears to come from the mailbox, with no indication of who actually sent it.
• Send on Behalf — send mail that shows both the sender and the mailbox.

Send As is invisible to recipients

A recipient cannot tell that someone other than the mailbox owner sent the message. Grant it where a shared mailbox genuinely needs to speak with one voice, and prefer Send on Behalf where accountability matters more than presentation.

Mail flow

Forwarding sends a copy of incoming mail elsewhere. Whether the original is also kept in the mailbox is a separate setting.

Forwarding is a standard data-exfiltration technique

A forward to an external address is how a compromised mailbox quietly leaks mail, and it is easy to miss because nothing else about the mailbox looks wrong. Treat an unexplained external forward as a security incident until proven otherwise, and check this tab when investigating one.

Mobile

Lists the devices synchronizing with the mailbox, and lets you remove one. Removing a device stops it synchronizing; it does not wipe the device.

Advanced

Per-mailbox storage limits, overriding the mailbox plan. Use the plan where you can — per-mailbox overrides accumulate into an estate nobody can reason about.

Archiving mailboxes

Where archiving is licensed, a mailbox can have an archive alongside it. Mail moved to the archive stops counting against the primary mailbox limit but remains available to the user.

Deleting a mailbox

Deleting a mailbox deletes its mail

The mailbox and its contents go. If the person is leaving and the mail may be needed — for a handover, a legal request, or simple continuity — export it or convert the mailbox to a shared one first.

Disabling the user account instead of deleting the mailbox stops access while keeping the mail, and is almost always the right first step.

Related

• Mailbox plans
• Storage usage
• Contacts and distribution lists

The tabs on a mailbox

Opening an on-premises mailbox gives a fixed set of tabs. The names are the product’s own, and they differ from the Exchange Online equivalents even where the function is the same — see Exchange Online mailboxes for that side.

Tab	What it controls
Mailbox Settings	General mailbox configuration
Mailbox Advanced	Advanced options, including storage limits
Mailbox Addresses	The email addresses the mailbox answers to
Mailbox Mailflow	Delivery, forwarding and restrictions
Mailbox Permissions	Who else may access this mailbox
Mailbox Member Of	Distribution lists and groups it belongs to
Mailbox Rules	Server-side rules
Mailbox OutOfOffice	Automatic replies
Mailbox Mobile and Mailbox Mobile Details	ActiveSync devices, and the detail of one
Setup Mailbox	The setup letter — connection details to send the user

Permissions here are not the same as delegation the user sets

Mailbox Permissions grants access administratively. A user can also delegate access themselves from their client, and that delegation does not appear here.

So this tab answers “what have we granted”, not “who can read this mailbox” — the second question needs both.

Mobile Details is where an ActiveSync problem is actually visible

The Mailbox Mobile list shows which devices are partnered. Mailbox Mobile Details shows the state of one — which is where a device that has stopped syncing shows up, as opposed to simply being absent.