Is Microsoft 365 Mailboxes safe to install?

SaferSkills independently audited Microsoft 365 Mailboxes (Agent Skill) and scored it 100/100 (green). The audit ran 55 deterministic rules across Security, Supply Chain, Maintenance, Transparency, and Community; it found 0 high-severity and 0 lower-severity findings. The full rule-by-rule trace and per-finding evidence are below. Free, methodology-open.

CategoryWeightCategory scoreContribution

Securityprompt, exec, net, exfil, eval

35%

100

35.0 pts

Supply chainhash, typosquat, maintainer, lockfile

20%

100

20.0 pts

Maintenancestaleness, pinning, CI

15%

100

15.0 pts

TransparencySKILL.md, perms, README

15%

100

15.0 pts

Communityinstalls, verify, response

15%

100

15.0 pts

Findings & checks · 0 flagged

Securityscore 100 · 0 findings

✓—All security checks passedNo findings in this category for the latest scan.pass

Supply chainscore 100 · 0 findings

✓—All supply chain checks passedNo findings in this category for the latest scan.pass

Maintenancescore 100 · 0 findings

✓—All maintenance checks passedNo findings in this category for the latest scan.pass

Transparencyscore 100 · 0 findings

✓—All transparency checks passedNo findings in this category for the latest scan.pass

Communityscore 100 · 0 findings

✓—All community checks passedNo findings in this category for the latest scan.pass

The primary manifest — the file an agent reads to learn what this artifact does.

msp-claude-plugins/m365/m365/skills/mailboxes/SKILL.md · 1 file

msp-claude-plugins/m365/m365/skills/mailboxes/SKILL.md7.2 KB · Markdown

name: "Microsoft 365 Mailboxes"

description: >

Use this skill when working with Microsoft 365 mailboxes - reading email,

searching messages, managing shared mailboxes, setting out-of-office replies,

checking mailbox size, or diagnosing mail flow issues. Covers Exchange Online

via Microsoft Graph for MSP technicians supporting customer email environments.

when_to_use: "When reading email, searching messages, managing shared mailboxes, setting out-of-office replies, checking mailbox size, or diagnosing mail flow issues"

triggers:

- m365 email

- m365 mailbox

- exchange online

- search email m365

- shared mailbox

- out of office m365

- mail flow issue

- email quota

- forward email m365

- inbox rules m365

Microsoft 365 Mailbox Management

Overview

Microsoft 365 mailboxes are managed through Exchange Online, accessible via Microsoft Graph. For MSPs, mailbox tasks range from diagnosing delivery failures and searching for lost emails to managing shared mailboxes and offboarding users. Graph provides a unified API across all mailbox types.

Mailbox Types

Type	Description	Common MSP Tasks
User Mailbox	Standard licensed user	Search, out-of-office, size, rules
Shared Mailbox	Team inbox, no license required	Access management, forwarding
Room/Equipment	Calendar resource booking	Availability, booking policies
Distribution Group	Email alias to multiple users	Membership, send-as

Graph API Patterns

List a User's Emails

GET /v1.0/users/{userId}/messages?$select=id,subject,from,receivedDateTime,isRead&$top=25&$orderby=receivedDateTime desc

Search for a Specific Email

GET /v1.0/users/{userId}/messages?$search="subject:invoice 2024"&$select=id,subject,from,receivedDateTime

Also supports KQL search operators:

$search="from:[email protected]" — by sender
$search="subject:urgent hasAttachments:true" — combined
$search="received>=2024-01-01" — date range

Get Message Details (with body)

GET /v1.0/users/{userId}/messages/{messageId}?$select=id,subject,from,body,receivedDateTime,attachments

Get Mailbox Settings (out-of-office, timezone)

GET /v1.0/users/{userId}/mailboxSettings

Response:

{
  "automaticRepliesSetting": {
    "status": "disabled",
    "internalReplyMessage": "",
    "externalReplyMessage": ""
  },
  "timeZone": "Eastern Standard Time",
  "language": { "locale": "en-US" }
}

Set Out-of-Office Reply

PATCH /v1.0/users/{userId}/mailboxSettings
Content-Type: application/json

{
  "automaticRepliesSetting": {
    "status": "alwaysEnabled",
    "internalReplyMessage": "<html>I'm out of office until Jan 15.</html>",
    "externalReplyMessage": "<html>I'm out of office. For urgent matters contact [email protected].</html>"
  }
}

Disable Out-of-Office Reply

PATCH /v1.0/users/{userId}/mailboxSettings
Content-Type: application/json

{
  "automaticRepliesSetting": { "status": "disabled" }
}

Get Mailbox Usage / Size

GET /v1.0/users/{userId}/mailFolders/inbox?$select=totalItemCount,sizeInBytes

For full mailbox statistics (requires Exchange admin permissions):

GET /v1.0/reports/getMailboxUsageDetail(period='D7')

Get Inbox Rules

GET /v1.0/users/{userId}/mailFolders/inbox/messageRules

Response shows rules that may affect mail delivery:

{
  "value": [
    {
      "id": "rule1",
      "displayName": "Move newsletters",
      "conditions": { "senderContains": ["newsletter"] },
      "actions": { "moveToFolder": "Newsletters" },
      "isEnabled": true
    }
  ]
}

Send an Email on Behalf of a User

POST /v1.0/users/{userId}/sendMail
Content-Type: application/json

{
  "message": {
    "subject": "Your IT support request has been resolved",
    "body": { "contentType": "HTML", "content": "<p>Your ticket #1234 is now closed.</p>" },
    "toRecipients": [{ "emailAddress": { "address": "[email protected]" } }]
  },
  "saveToSentItems": true
}

Shared Mailbox Management

Add User Access to Shared Mailbox

Shared mailbox access is managed via Microsoft 365 admin or Exchange PowerShell, not directly via Graph mailbox endpoints. Use Graph group membership or delegate access patterns.

List Users With Shared Mailbox Access

Access is represented as mailboxPermissions — check via admin APIs or Exchange PowerShell:

Get-MailboxPermission -Identity "[email protected]" | Where-Object { $_.AccessRights -eq "FullAccess" }

Mail Flow Diagnostics

Check Recent Delivery Failures

Look for NDRs (Non-Delivery Reports) in the user's inbox or sent items:

GET /v1.0/users/{userId}/messages?$filter=senderEmailAddress/address eq '[email protected]'&$select=subject,receivedDateTime,body

Common Delivery Failure Reasons

NDR Code	Meaning	Resolution
`5.1.1`	Recipient doesn't exist	Verify UPN / check aliases
`5.1.8`	Sender blocked (spam)	Review anti-spam policy
`5.2.2`	Mailbox full	Check quota, remove items
`5.7.1`	Unauthorized relay	SMTP auth settings
`5.7.606`	Sender IP blocked	Submit to Microsoft for delisting

Common MSP Workflows

Lost Email Investigation

Confirm exact sender address and approximate date
Search user's mailbox including Junk and Deleted folders
Check inbox rules that might divert messages
Review message trace in Microsoft 365 admin (requires admin access)
Check anti-spam quarantine if IT admin access available

Offboarding Mailbox Handling

Option A: Convert to shared mailbox (no license needed, data accessible)

Disable user account
Convert mailbox to shared via admin center or Graph
Grant departing user's manager full access

Option B: Forward and archive

Set auto-forward to manager
Export mailbox to PST/archive
Remove license after retention period

Option C: Auto-reply and close

Set out-of-office explaining user has left
Leave mailbox active during handover period
Remove license after business decides archival approach

Error Handling

Error	Cause	Resolution
`MailboxNotEnabledForRESTAPI`	User has no Exchange license	Assign Exchange/M365 license
`ErrorItemNotFound`	Message ID expired or moved	Search by subject/date instead
`AuthenticationError`	Token expired	Re-authenticate via OAuth flow
`TooManyRequests`	Graph throttling (429)	Retry with exponential backoff
`Forbidden (403)`	Missing Mail.Read permission	Check app registration

Permissions Required

Task	Microsoft Graph Permission
Read emails	`Mail.Read` or `Mail.ReadWrite`
Send email	`Mail.Send`
Mailbox settings	`MailboxSettings.ReadWrite`
All users' mail (admin)	`Mail.Read` (delegated + admin consent)

M365 Users - Account status, disable, license
M365 Calendar - Calendar and out-of-office coordination
M365 Security - Forwarding rule abuse, account compromise signs
M365 API Patterns - Auth, pagination, search syntax

Microsoft 365 Mailboxes— agent skill

Is Microsoft 365 Mailboxes safe to install?

Microsoft 365 Mailbox Management

Overview

Mailbox Types

Graph API Patterns

List a User's Emails

Search for a Specific Email

Get Message Details (with body)

Get Mailbox Settings (out-of-office, timezone)

Set Out-of-Office Reply

Disable Out-of-Office Reply

Get Mailbox Usage / Size

Get Inbox Rules

Send an Email on Behalf of a User

Shared Mailbox Management

Add User Access to Shared Mailbox

List Users With Shared Mailbox Access

Mail Flow Diagnostics

Check Recent Delivery Failures

Common Delivery Failure Reasons

Common MSP Workflows

Lost Email Investigation

Offboarding Mailbox Handling

Error Handling

Permissions Required

Audit the pieces. Scan the whole. Decide.

Is Microsoft 365 Mailboxes safe to install?

Microsoft 365 Mailbox Management

Overview

Mailbox Types

Graph API Patterns

List a User's Emails

Search for a Specific Email

Get Message Details (with body)

Get Mailbox Settings (out-of-office, timezone)

Set Out-of-Office Reply

Disable Out-of-Office Reply

Get Mailbox Usage / Size

Get Inbox Rules

Send an Email on Behalf of a User

Shared Mailbox Management

Add User Access to Shared Mailbox

List Users With Shared Mailbox Access

Mail Flow Diagnostics

Check Recent Delivery Failures

Common Delivery Failure Reasons

Common MSP Workflows

Lost Email Investigation

Offboarding Mailbox Handling

Error Handling

Permissions Required

Related Skills

Audit the pieces. Scan the whole. Decide.