Mailboxes

Overview

A mailbox in TenantCore is a shared mailbox provisioned on a verified custom domain in a Microsoft 365 tenant. Each domain supports up to 3 mailboxes. Mailboxes are created as shared mailboxes in Exchange Online and do not consume a Microsoft 365 license. Send limits are opt-in, not mandatory. Mailboxes are created without an enforced send limit by design. If you have fewer domains and want higher per-mailbox volume, you can leave limits unenforced and mailboxes will send without restriction. Send limit enforcement is a two-step process:

Set the limit — use PATCH /v1/tenants/{tenant_id}/mailboxes/{mailbox_id} to store a daily_send_limit value per mailbox
Provision enforcement — use POST /v1/tenants/{tenant_id}/mailbox-limits to write the Exchange transport rule that enforces it

Setting a daily_send_limit on a mailbox without provisioning enforcement saves the value but does not restrict sending. The Exchange transport rule is what enforces the ceiling at the infrastructure level.

Exchange Online propagation after provisioning a mailbox takes 2 to 5 minutes. The mailbox will not be immediately available for sending after the API call returns.

List mailboxes

Returns all mailboxes across all domains on a tenant.

GET /v1/tenants/{tenant_id}/mailboxes

Path parameters

Parameter	Type	Description
`tenant_id`	string	The Microsoft tenant GUID

Example request

curl https://api.tenantcore.io/v1/tenants/xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx/mailboxes \
  -H "Authorization: Bearer tc_live_your_key"

Example response

{
  "tenant_id": "xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx",
  "mailboxes": [
    {
      "id": "uuid",
      "display_name": "John Doe",
      "primary_smtp": "john@mail.acmecorp.com",
      "user_principal_name": "john@mail.acmecorp.com",
      "mail_nickname": "john",
      "account_enabled": true,
      "daily_send_limit": 25,
      "sends_today": 12,
      "blocked_at": null,
      "created_at": "2025-01-20T10:00:00Z",
      "domain_name": "mail.acmecorp.com",
      "tenant_name": "Acme Corp"
    }
  ],
  "count": 1
}

Response fields

Field	Type	Description
`primary_smtp`	string	The mailbox email address
`account_enabled`	boolean	Whether the account is enabled in Azure AD
`daily_send_limit`	number	Configured daily send cap (1 to 25)
`sends_today`	number	Emails sent today as reported by Exchange message trace
`blocked_at`	timestamp or null	When the mailbox was blocked by enforcement, or `null` if not blocked

Errors

Status	Code	Description
`404`	`tenant_not_found`	Tenant does not exist or belongs to a different account

Provision mailboxes

Creates one or more shared mailboxes on a verified domain. Up to 3 mailboxes per domain. All mailboxes in the request must belong to the same domain.

POST /v1/tenants/{tenant_id}/mailboxes

Path parameters

Parameter	Type	Description
`tenant_id`	string	The Microsoft tenant GUID

Request body

{
  "domain": "mail.acmecorp.com",
  "account_password": "SecureP@ssw0rd!",
  "mailboxes": [
    { "name": "John Doe", "email": "john@mail.acmecorp.com" },
    { "name": "Jane Doe", "email": "jane@mail.acmecorp.com" }
  ]
}

Field	Type	Required	Description
`domain`	string	Yes	The verified domain to create mailboxes on
`account_password`	string	Yes	Initial password for the underlying user account. Min 8 characters. Must meet Microsoft’s complexity requirements.
`mailboxes`	array	Yes	List of mailboxes to create. Max 3 total per domain including existing.
`mailboxes[].name`	string	Yes	Display name for the mailbox
`mailboxes[].email`	string	Yes	Full email address. Must end with `@{domain}`.

Example request

curl -X POST \
  https://api.tenantcore.io/v1/tenants/xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx/mailboxes \
  -H "Authorization: Bearer tc_live_your_key" \
  -H "Content-Type: application/json" \
  -d '{
    "domain": "mail.acmecorp.com",
    "account_password": "SecureP@ssw0rd!",
    "mailboxes": [
      { "name": "Sales Outreach", "email": "sales@mail.acmecorp.com" }
    ]
  }'

Example response

{
  "created_count": 1,
  "exists_count": 0,
  "failed_count": 0,
  "results": [
    {
      "status": "created",
      "name": "Sales Outreach",
      "email": "sales@mail.acmecorp.com",
      "details": {
        "display_name": "Sales Outreach",
        "primary_smtp": "sales@mail.acmecorp.com",
        "user_principal_name": "sales@mail.acmecorp.com",
        "alias": "sales"
      }
    }
  ]
}

Result statuses per mailbox

Status	Meaning
`created`	Mailbox was successfully provisioned
`exists`	Mailbox already exists, no action taken
`failed`	Provisioning failed for this mailbox, check `error` field in result

Prerequisites

The domain must be verified in Microsoft 365
Exchange bootstrap must be ready on the tenant
SMTP AUTH must be enabled on the tenant

Errors

Status	Code	Description
`400`	`mailbox_limit_reached`	Domain already has 3 mailboxes
`400`	—	Invalid email domain, duplicate emails, or weak password
`404`	`tenant_not_found`	Tenant does not exist or belongs to a different account
`404`	`domain_not_found`	Domain not registered on this tenant

Update mailbox

Updates the display name or daily send limit of a mailbox. Updating daily_send_limit stores the value in TenantCore but does not provision Exchange enforcement on its own. To activate enforcement at the Exchange level, call POST /v1/tenants/{tenant_id}/mailbox-limits after updating the limit.

PATCH /v1/tenants/{tenant_id}/mailboxes/{mailbox_id}

Path parameters

Parameter	Type	Description
`tenant_id`	string	The Microsoft tenant GUID
`mailbox_id`	string	The TenantCore mailbox UUID (from list mailboxes)

Request body

{
  "display_name": "New Display Name",
  "daily_send_limit": 20
}

Field	Type	Required	Description
`display_name`	string	No	New display name for the mailbox
`daily_send_limit`	number	No	Daily send cap between 1 and 25. Stores the value in TenantCore. Exchange enforcement must be provisioned separately.

At least one field must be provided. Example request

curl -X PATCH \
  https://api.tenantcore.io/v1/tenants/xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx/mailboxes/mailbox-uuid \
  -H "Authorization: Bearer tc_live_your_key" \
  -H "Content-Type: application/json" \
  -d '{"daily_send_limit": 20}'

Example response

{
  "status": "updated",
  "mailbox": {
    "id": "mailbox-uuid",
    "display_name": "Sales Outreach",
    "primary_smtp": "sales@mail.acmecorp.com",
    "daily_send_limit": 20,
    "sends_today": 12,
    "account_enabled": true
  }
}

Errors

Status	Code	Description
`400`	`invalid_send_limit`	`daily_send_limit` is outside the 1 to 25 range
`400`	`no_updates`	Request body contained no recognised fields
`404`	`tenant_not_found`	Tenant does not exist or belongs to a different account
`404`	`mailbox_not_found`	Mailbox does not exist on this tenant

Set enforcement

Saves a send limit policy and provisions the Exchange Online transport rule that enforces it. This is the step that activates the hard ceiling at the infrastructure level. Until this is called, daily_send_limit values on mailboxes are stored but not enforced by Exchange. Enforcement is scoped at the domain level. Apply it to a specific domain or tenant-wide across all domains at once.

POST /v1/tenants/{tenant_id}/mailbox-limits

Path parameters

Parameter	Type	Description
`tenant_id`	string	The Microsoft tenant GUID

Request body

{
  "daily_send_limit": 25,
  "domain_scope": "mail.acmecorp.com"
}

Field	Type	Required	Description
`daily_send_limit`	number	Yes	The enforced daily send cap between 1 and 25
`domain_scope`	string	No	The domain to scope enforcement to. Omit to apply tenant-wide across all domains.

Example request — single domain

curl -X POST \
  https://api.tenantcore.io/v1/tenants/xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx/mailbox-limits \
  -H "Authorization: Bearer tc_live_your_key" \
  -H "Content-Type: application/json" \
  -d '{
    "daily_send_limit": 25,
    "domain_scope": "mail.acmecorp.com"
  }'

Example request — tenant-wide

curl -X POST \
  https://api.tenantcore.io/v1/tenants/xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx/mailbox-limits \
  -H "Authorization: Bearer tc_live_your_key" \
  -H "Content-Type: application/json" \
  -d '{"daily_send_limit": 25}'

Example response

{
  "status": "success",
  "tenant_id": "xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx",
  "daily_send_limit": 25,
  "domain_scope": "mail.acmecorp.com",
  "scope_label": "mail.acmecorp.com",
  "policy": {},
  "provisioning": {}
}

Errors

Status	Code	Description
`400`	`invalid_send_limit`	`daily_send_limit` is outside the 1 to 25 range
`404`	`tenant_not_found`	Tenant does not exist or belongs to a different account
`404`	`domain_not_found`	Specified `domain_scope` is not registered on this tenant
`409`	`exchange_bootstrap_not_ready`	Exchange bootstrap has not completed for this tenant

Get enforcement policy

Returns the current limit policy for a tenant or specific domain.

GET /v1/tenants/{tenant_id}/mailbox-limits

Path parameters

Parameter	Type	Description
`tenant_id`	string	The Microsoft tenant GUID

Query parameters

Parameter	Type	Description
`domain_scope`	string	Optional. Pass a domain name to retrieve the policy for that domain. Omit for the tenant-wide policy.

Example request

curl "https://api.tenantcore.io/v1/tenants/xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx/mailbox-limits?domain_scope=mail.acmecorp.com" \
  -H "Authorization: Bearer tc_live_your_key"

Errors

Status	Code	Description
`404`	`tenant_not_found`	Tenant does not exist or belongs to a different account
`404`	`policy_not_found`	No limit policy has been set for this scope

Get mailbox usage

Returns daily send counts, limit status, and block state for a specific mailbox.

GET /v1/tenants/{tenant_id}/mailboxes/{mailbox_id}/usage

Path parameters

Parameter	Type	Description
`tenant_id`	string	The Microsoft tenant GUID
`mailbox_id`	string	The TenantCore mailbox UUID

Example request

curl https://api.tenantcore.io/v1/tenants/xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx/mailboxes/mailbox-uuid/usage \
  -H "Authorization: Bearer tc_live_your_key"

Example response

{
  "mailbox_id": "mailbox-uuid",
  "primary_smtp": "sales@mail.acmecorp.com",
  "display_name": "Sales Outreach",
  "account_enabled": true,
  "daily_send_limit": 25,
  "sends_today": 18,
  "remaining_sends": 7,
  "is_blocked": false,
  "blocked_at": null,
  "utilization_pct": 72.0
}

Response fields

Field	Type	Description
`daily_send_limit`	number	The configured cap
`sends_today`	number	Emails sent today from Exchange message trace
`remaining_sends`	number	`daily_send_limit - sends_today`, floored at 0
`is_blocked`	boolean	`true` if enforcement has blocked this mailbox
`blocked_at`	timestamp or null	When the block was applied
`utilization_pct`	number	`sends_today / daily_send_limit x 100`, rounded to 1 decimal

Errors

Status	Code	Description
`404`	`tenant_not_found`	Tenant does not exist or belongs to a different account
`404`	`mailbox_not_found`	Mailbox does not exist on this tenant

Overview

Authentication

Endpoints

Overview

List mailboxes

Provision mailboxes

Update mailbox

Set enforcement

Get enforcement policy

Get mailbox usage

​Overview

​List mailboxes

​Provision mailboxes

​Update mailbox

​Set enforcement

​Get enforcement policy

​Get mailbox usage

Overview

List mailboxes

Provision mailboxes

Update mailbox

Set enforcement

Get enforcement policy

Get mailbox usage