> ## Documentation Index
> Fetch the complete documentation index at: https://docs.tenantcore.io/llms.txt
> Use this file to discover all available pages before exploring further.

# Create Mailboxes

> Create TenantCore-managed sending mailboxes under a domain in a connected Microsoft 365 tenant.

# Create Mailboxes

TenantCore can create sending mailboxes under domains already registered to a connected tenant.

Each domain supports up to **3 mailboxes**.

## Before you begin

You need:

* a connected Microsoft 365 tenant
* a domain already added to that tenant
* available mailbox capacity
* a domain sufficiently prepared for the workflow you intend to use

## Create a mailbox

1. Open **Mailboxes** or the mailbox view for the domain.
2. Choose **Create mailbox**.
3. Enter the mailbox details requested by TenantCore.
4. Submit the request.

TenantCore creates the mailbox in Microsoft 365 and creates the corresponding TenantCore mailbox resource.

## After creation

The mailbox can then be used for:

* password access/reset
* optional MFA setup
* send-limit configuration
* Outlook delegation
* sending-platform connection
* monitoring and Reports

## Credential handling

TenantCore protects mailbox credentials through its secure credential-vault workflow.

Do not build an external spreadsheet-based password process around mailbox creation.

Use TenantCore's credential controls when you need the password.

## Mailbox ownership

Every mailbox is attached to:

```text theme={null}
TenantCore account
      ↓
Tenant
      ↓
Domain
      ↓
Mailbox
```

This relationship is also enforced by the Complete API.

An arbitrary external mailbox cannot be submitted to TenantCore and managed as though it belonged to the account.

## If creation fails

Check:

* the domain still belongs to the connected tenant
* mailbox capacity has not been reached
* Microsoft/Exchange access is healthy
* the address is not already in use
* TenantCore has the required application permissions

Correct the underlying condition and retry the supported TenantCore workflow.