Domains

Overview

A domain is a custom sending domain added to a Microsoft 365 tenant. Microsoft imposes no hard limit on custom domains per tenant. TenantCore recommends 12 domains per tenant as the optimal structure for cold email infrastructure. TenantCore generates all DNS records required to configure the domain at your registrar and queries live DNS status on each domain so you can monitor authentication health across your infrastructure. The standard TenantCore structure is:

1 tenant
└── 12 domains
    └── 3 mailboxes each = 36 mailboxes total

Domains must be verified in Microsoft 365 before mailboxes can be provisioned on them. Add the domain first, configure the DNS records at your registrar, then verify via the TenantCore app.

List domains

Returns all custom domains registered on a tenant, including live DNS health status.

GET /v1/tenants/{tenant_id}/domains

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/domains \
  -H "Authorization: Bearer tc_live_your_key"

Example response

{
  "tenant_id": "xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx",
  "domains": [
    {
      "id": "uuid",
      "domain_name": "mail.acmecorp.com",
      "is_default": true,
      "is_verified": true,
      "spf_status": "v=spf1 include:spf.protection.outlook.com -all",
      "dkim_status": "healthy",
      "dmarc_status": "v=DMARC1; p=quarantine; rua=mailto:dmarc@acmecorp.com",
      "mx_status": "acmecorp-com.mail.protection.outlook.com.",
      "last_checked": "2025-04-20T08:00:00Z"
    }
  ],
  "count": 1
}

Response fields

Field	Type	Description
`domain_name`	string	The custom domain
`is_default`	boolean	Whether this is the tenant’s primary domain
`is_verified`	boolean	Whether Microsoft has verified this domain
`spf_status`	string	Raw SPF TXT record, or `"missing"`
`dkim_status`	string	`"healthy"`, `"partial"`, `"missing"`, or selector detail
`dmarc_status`	string	Raw DMARC TXT record, or `"missing"`
`mx_status`	string	Raw MX record, or `"missing"`
`last_checked`	timestamp	When DNS was last queried

Errors

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

Add domain

Adds a custom domain to a tenant in Microsoft 365 and returns the DNS records you need to configure at your registrar. The domain is created in Microsoft but remains unverified until you add the required DNS records and trigger verification.

POST /v1/tenants/{tenant_id}/domains

Path parameters

Parameter	Type	Description
`tenant_id`	string	The Microsoft tenant GUID

Request body

{
  "domain": "mail.acmecorp.com"
}

Field	Type	Required	Description
`domain`	string	Yes	The custom domain to add. Must be a valid domain. `.onmicrosoft.com` domains are not allowed.

Example request

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

Example response

{
  "status": "success",
  "tenant_id": "xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx",
  "domain": {
    "domain_name": "mail.acmecorp.com",
    "is_default": false,
    "is_verified": false
  },
  "verification_dns_records": [
    {
      "recordType": "domainDnsTxtRecord",
      "label": "@",
      "text": "MS=ms12345678",
      "ttl": 3600
    }
  ],
  "service_configuration_records": [
    {
      "recordType": "domainDnsMxRecord",
      "label": "@",
      "mailExchange": "mail.acmecorp.com.mail.protection.outlook.com",
      "preference": 0,
      "ttl": 3600
    }
  ],
  "live_dns_status": {
    "spf_status": "missing",
    "dkim_status": "missing",
    "dmarc_status": "missing",
    "mx_status": "missing"
  },
  "dkim_verification_state": {
    "status": "missing",
    "message": "missing (selector1, selector2)"
  }
}

After adding a domain

Add the verification_dns_records TXT record at your registrar
Add all service_configuration_records (MX, CNAME for DKIM, TXT for SPF)
Wait for DNS propagation (typically 5 to 30 minutes, up to 48 hours)
Trigger domain verification from the TenantCore app

Errors

Status	Code	Description
`400`	`domain_limit_reached`	Tenant already has 12 domains
`400`	—	Invalid domain format or `.onmicrosoft.com` domain
`404`	`tenant_not_found`	Tenant does not exist or belongs to a different account

Verify domain

Triggers Microsoft domain verification after DNS records have been configured. This is required before mailboxes can be created and sending can begin.


POST /v1/tenants/{tenant_id}/domains/{domain_name}/verify

Path parameters

Parameter	Type	Description
`tenant_id`	string	The Microsoft tenant GUID
`domain_name`	string	The custom domain name

Example request

curl -X POST \
  https://api.tenantcore.io/v1/tenants/xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx/domains/mail.acmecorp.com/verify \
  -H "Authorization: Bearer tc_live_your_key"

Example response

{
  "status": "success",
  "domain_name": "mail.acmecorp.com",
  "is_verified": true,
  "message": "Domain successfully verified in Microsoft 365"
}

Errors

Status	Code	Description
`400`	`verification_failed`	DNS records not yet propagated or incorrect
`404`	`domain_not_found`	Domain is not registered on this tenant

Enable DKIM

Enables DKIM signing for a verified domain. This is required for full email authentication and deliverability.

POST /v1/tenants/{tenant_id}/domains/{domain_name}/enable-dkim

Path parameters

Parameter	Type	Description
`tenant_id`	string	The Microsoft tenant GUID
`domain_name`	string	The custom domain name

Example request

curl -X POST \
  https://api.tenantcore.io/v1/tenants/xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx/domains/mail.acmecorp.com/enable-dkim \
  -H "Authorization: Bearer tc_live_your_key"

Example response

{
  "status": "success",
  "domain_name": "mail.acmecorp.com",
  "dkim_status": "enabled",
  "message": "DKIM successfully enabled"
}

Errors

Status	Code	Description
`400`	`dkim_not_ready`	Required CNAME records not found in DNS
`404`	`domain_not_found`	Domain is not registered on this tenant

Get DKIM status

Returns the current DKIM state for a domain. Useful for polling until DNS propagation is complete and DKIM can be enabled.

GET /v1/tenants/{tenant_id}/domains/{domain_name}/dkim-status

Path parameters

Parameter	Type	Description
`tenant_id`	string	The Microsoft tenant GUID
`domain_name`	string	The custom domain name

Example request

curl https://api.tenantcore.io/v1/tenants/xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx/domains/mail.acmecorp.com/dkim-status \
  -H "Authorization: Bearer tc_live_your_key"

Example response

{
  "domain_name": "mail.acmecorp.com",
  "dkim_status": "pending",
  "selectors": {
    "selector1": "missing",
    "selector2": "propagated"
  },
  "ready_to_enable": false,
  "last_checked": "2025-04-20T08:00:00Z"
}

Response fields

Field	Type	Description
`dkim_status`	string	`"pending"`, `"ready"`, `"enabled"`
`selectors`	object	Status of selector1 and selector2
`ready_to_enable`	boolean	Whether DKIM can be enabled
`last_checked`	timestamp	Last DNS check

Get DNS records

Returns the stored DNS records and current DNS health for a specific domain. This does not trigger a live DNS re-check — it returns what was last recorded. Use the TenantCore app to trigger a fresh DNS check.

GET /v1/tenants/{tenant_id}/domains/{domain_name}/dns

Path parameters

Parameter	Type	Description
`tenant_id`	string	The Microsoft tenant GUID
`domain_name`	string	The custom domain name, e.g. `mail.acmecorp.com`

Example request

curl https://api.tenantcore.io/v1/tenants/xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx/domains/mail.acmecorp.com/dns \
  -H "Authorization: Bearer tc_live_your_key"

Example response

{
  "tenant_id": "xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx",
  "domain_name": "mail.acmecorp.com",
  "is_default": false,
  "is_verified": true,
  "dns_status": {
    "spf": "v=spf1 include:spf.protection.outlook.com -all",
    "dkim": "healthy",
    "dmarc": "v=DMARC1; p=quarantine",
    "mx": "mail.acmecorp.com.mail.protection.outlook.com."
  },
  "verification_dns_records": [],
  "service_configuration_records": [
    {
      "recordType": "domainDnsMxRecord",
      "label": "@",
      "mailExchange": "mail.acmecorp.com.mail.protection.outlook.com",
      "preference": 0,
      "ttl": 3600
    },
    {
      "recordType": "domainDnsCnameRecord",
      "label": "selector1._domainkey",
      "canonicalName": "selector1-mail-acmecorp-com._domainkey.acmecorp.onmicrosoft.com",
      "ttl": 3600
    },
    {
      "recordType": "domainDnsCnameRecord",
      "label": "selector2._domainkey",
      "canonicalName": "selector2-mail-acmecorp-com._domainkey.acmecorp.onmicrosoft.com",
      "ttl": 3600
    }
  ],
  "last_checked": "2025-04-20T08:00:00Z"
}

Errors

Status	Code	Description
`404`	`tenant_not_found`	Tenant does not exist or belongs to a different account
`404`	`domain_not_found`	Domain is not registered on this tenant

Overview

Authentication

Endpoints

Overview

List domains

Add domain

Verify domain

Enable DKIM

Get DKIM status

Get DNS records

​Overview

​List domains

​Add domain

​Verify domain

​Enable DKIM

​Get DKIM status

​Get DNS records

Overview

List domains

Add domain

Verify domain

Enable DKIM

Get DKIM status

Get DNS records