casMailboxPlans

Client Access Plans. Default protocol settings new mailboxes inherit by plan. The casMailboxPlans entity set lives under /exchange/v1.0/casMailboxPlans in the Mailbox settings category.

Fact	Value
Path	/exchange/v1.0/casMailboxPlans
Category	Mailbox settings
Tier	Tier 9, Hybrid and organization
Read role	OrganizationConfig.Read.All (Community)
Write role	OrganizationConfig.ReadWrite.All (Enterprise)
Backing cmdlets	Get-CASMailboxPlan, Set-CASMailboxPlan

Routes

Method	Path	Synopsis	Role	Plan
GET	/exchange/v1.0/casMailboxPlans	List casMailboxPlans entries.	OrganizationConfig.Read	Community
GET	/exchange/v1.0/casMailboxPlans/{key}	Get a single casMailboxPlans entry by Identity.	OrganizationConfig.Read	Community
PATCH	/exchange/v1.0/casMailboxPlans/{key}	PATCH /casMailboxPlans/{key} - update the plan’s client-access protocol defaults via Set-CASMailboxPlan. Body keys subset of (e.g. { “popEnabled”: false, “imapEnabled”: false }). Returns 200 + the refreshed plan. ?dryRun=true previews (-WhatIf).	OrganizationConfig.ReadWrite	Enterprise

GET /exchange/v1.0/casMailboxPlans

List casMailboxPlans entries.

Backing cmdlet: Get-CASMailboxPlan. Role: OrganizationConfig.Read (Community).

Parameter	In	Type	Required	Description
all	query	bool (switch)		Return all results instead of the EXO default of 1000. Maps -ResultSize Unlimited on Get-CASMailboxPlan; prevents silent truncation in large tenants.

List CAS mailbox plans

Lists every CAS (Client Access Services) mailbox plan via Get-CASMailboxPlan. Each plan carries the protocol-access defaults (POP/IMAP/MAPI/EWS/OWA/ActiveSync/ECP) inherited by mailboxes provisioned under the matching mailbox plan. One plan per license SKU, tenant-wide.

GET /exchange/v1.0/casMailboxPlans HTTP/1.1
Authorization: Bearer {token}

HTTP/1.1 200 OK
Content-Type: application/json; charset=utf-8

{
  "@odata.context": "https://api.contoso.com/exchange/v1.0/$metadata#casMailboxPlans",
  "value": [
    {
      "Id": "ExchangeOnline-11111111-1111-1111-1111-111111111111",
      "Name": "ExchangeOnline-11111111-1111-1111-1111-111111111111",
      "DisplayName": "ExchangeOnline",
      "Identity": "ExchangeOnline-11111111-1111-1111-1111-111111111111",
      "Guid": "a1b2c3d4-1111-2222-3333-444444444444",
      "MailboxPlanIndex": null,
      "PrimarySmtpAddress": null,
      "ActiveSyncEnabled": true,
      "ECPEnabled": true,
      "EwsEnabled": 1,
      "ImapEnabled": true,
      "MAPIEnabled": true,
      "OWAEnabled": true,
      "OwaMailboxPolicy": "OwaMailboxPolicy-Default",
      "PopEnabled": true,
      "WhenCreatedUTC": "2026-03-30T14:03:03Z",
      "WhenChangedUTC": "2026-03-30T14:04:28Z"
    }
  ]
}

Notes: Live-captured against EXO and sanitized (plan GUIDs + identifiers replaced). The tenant returned 4 plans; one representative plan shown.

Related: GET /exchange/v1.0/casMailboxPlans/{key}, GET /exchange/v1.0/mailboxPlans

GET /exchange/v1.0/casMailboxPlans/{key}

Get a single casMailboxPlans entry by Identity.

Backing cmdlet: Get-CASMailboxPlan. Role: OrganizationConfig.Read (Community).

Get a CAS mailbox plan by key

Fetches a single CAS mailbox plan by its Identity via Get-CASMailboxPlan. A bad key returns 404 (the controller matches the requested key against Id/Identity/Name/Guid rather than blindly returning the first row).

GET /exchange/v1.0/casMailboxPlans/{key} HTTP/1.1
Authorization: Bearer {token}

HTTP/1.1 200 OK
Content-Type: application/json; charset=utf-8

{
  "@odata.context": "https://api.contoso.com/exchange/v1.0/$metadata#casMailboxPlans/$entity",
  "Id": "ExchangeOnline-11111111-1111-1111-1111-111111111111",
  "Name": "ExchangeOnline-11111111-1111-1111-1111-111111111111",
  "DisplayName": "ExchangeOnline",
  "Identity": "ExchangeOnline-11111111-1111-1111-1111-111111111111",
  "Guid": "a1b2c3d4-1111-2222-3333-444444444444",
  "MailboxPlanIndex": null,
  "PrimarySmtpAddress": null,
  "ActiveSyncEnabled": true,
  "ECPEnabled": true,
  "EwsEnabled": 1,
  "ImapEnabled": true,
  "MAPIEnabled": true,
  "OWAEnabled": true,
  "OwaMailboxPolicy": "OwaMailboxPolicy-Default",
  "PopEnabled": true,
  "WhenCreatedUTC": "2026-03-30T14:03:03Z",
  "WhenChangedUTC": "2026-03-30T14:04:28Z"
}

Notes: Live-captured against EXO and sanitized.

Related: GET /exchange/v1.0/casMailboxPlans, PATCH /exchange/v1.0/casMailboxPlans/{key}

PATCH /exchange/v1.0/casMailboxPlans/{key}

PATCH /casMailboxPlans/{key} - update the plan’s client-access protocol defaults via Set-CASMailboxPlan. Body keys subset of (e.g. { “popEnabled”: false, “imapEnabled”: false }). Returns 200 + the refreshed plan. ?dryRun=true previews (-WhatIf).

Backing cmdlet: Set-CASMailboxPlan. Role: OrganizationConfig.ReadWrite (Enterprise).

Parameter	In	Type	Required	Description
activeSyncEnabled	body
ecpEnabled	body
ewsEnabled	body
imapEnabled	body
mapiEnabled	body
owaEnabled	body
owaMailboxPolicy	body
popEnabled	body
dryRun	query	bool (switch)

Update CAS mailbox plan protocol defaults (tenant capability gate)

Updates a plan’s client-access protocol defaults via Set-CASMailboxPlan. Body keys: activeSyncEnabled, ecpEnabled, ewsEnabled, imapEnabled, mapiEnabled, oWAEnabled, owaMailboxPolicy, popEnabled. On success returns 200 + the refreshed plan. NOTE: on some tenants/app-only principals Set-CASMailboxPlan is gated server-side and returns the generic EXO ‘server side error’ (surfaced here as a 500 ExchangeCommandFailed envelope) - the wiring is correct; the cmdlet is simply not permitted for the calling principal on that tenant.

PATCH /exchange/v1.0/casMailboxPlans/{key} HTTP/1.1
Authorization: Bearer {token}
Content-Type: application/json

{
  "popEnabled": false,
  "imapEnabled": false
}

HTTP/1.1 500 Internal Server Error
Content-Type: application/json; charset=utf-8

{
  "error": {
    "code": "ExchangeCommandFailed",
    "message": "Cmdlet 'Set-CASMailboxPlan' failed: A server side error has occurred because of which the operation could not be completed. Please try again after some time. If the problem still persists, please reach out to MS support.",
    "target": null,
    "innerError": {
      "cmdlet": "Set-CASMailboxPlan"
    }
  }
}

Notes: Live-captured 2026-05-29 (sanitized). Both the real PATCH and the ?dryRun=true (-WhatIf) form return this identical generic EXO error, confirming it is a service-side capability gate on Set-CASMailboxPlan rather than a -WhatIf or code issue.

Related: GET /exchange/v1.0/casMailboxPlans/{key}

?dryRun=true previews of any write stay on Community.