What is Microsoft Outlook? An Overview of Email and Calendars Available in M365 E3/E5 for Beginners
About This Article
This article is generated using an automated workflow powered by generative AI. It is based on official Microsoft documentation for Microsoft 365, Exchange Online, and Outlook, structured so that general users, administrative staff, and IT administrators can understand what is happening behind the Outlook interface.Verification Status: 📘 Verified with Official Microsoft Documentation / Not Verified on Physical Devices
Outlook is not merely an email client. In a professional environment, it serves as the entry point for handling:Emails, calendars, meeting invitations, contacts, and shared mailboxes.Furthermore, in a corporate Microsoft 365 environment, the core data for emails and calendars resides primarily on the Exchange Online side.
- Clarifying Terminology First
- Relationship between Outlook and Exchange Online
- How to approach this in M365 E3/E5?
- The new Outlook and classic Outlook are not the same
- The flow from email reception to calendar reflection
- Try first: add search criteria one by one
- Do not start inbox rules with deletion
- PowerShell: inspect files without interacting with Outlook
- Microsoft Graph: First, read your profile
- If you are in an environment where you can use Copilot
- Common use cases at work
- Key points for IT departments and administrators to verify
- Official and primary sources
Clarifying Terminology First
| Term | Beginner-Friendly Definition |
|---|---|
| Outlook | App or screen for viewing emails and calendars |
| Exchange Online | Cloud service that hosts mailboxes and calendars on Microsoft 365 |
| Mailbox | Storage area that holds your emails, calendar, and other items |
| Shared mailbox | Feature that allows multiple users to manage department or team email addresses |
| Inbox rule | Mechanism that automatically moves and categorizes emails matching specified conditions |
| Microsoft Graph | API used by programs to access and manage Microsoft 365 data |
Instead of thinking that emails reside in Outlook,understanding that Outlook accesses and displays emails hosted in Exchange Onlinemakes it easier to understand why emails remain accessible after replacing a PC and why the web and desktop versions share the same calendar.
Relationship between Outlook and Exchange Online
flowchart LR
EXO[(Exchange Online\nメールボックス・予定表)]
WEB[Outlook on the web]
NEW[新しい Outlook]
CLASSIC[クラシック Outlook]
MOBILE[Outlook モバイル]
TEAMS[Teams / 会議]
WEB <--> EXO
NEW <--> EXO
CLASSIC <--> EXO
MOBILE <--> EXO
TEAMS <--> EXO
The important point here isnot to consider the Outlook client type and Exchange Online as the same thing.
How to approach this in M365 E3/E5?
While both Microsoft 365 E3 and E5 include Microsoft 365 Apps and Exchange Online, the actual configuration may vary depending on the licensing SKU, region, and whether Teams is included. Please verify your tenant's licensing terms in the admin center during deployment.
| Perspective | M365 E3 | M365 E5 | Mnemonic |
|---|---|---|---|
| Outlook on the web | ○ | ○ | Accessed via browser |
| Microsoft 365 desktop apps | ○ | ○ | Verify the provisioning conditions for Apps including Outlook |
| Exchange Online | ○ | ○ | Email infrastructure |
| Advanced Security/Compliance | Verify contract scope | Some configurations offer broader functionality on the E5 side | Do not judge based on Outlook alone |
| Copilot | Verify license rights separately | Verify license rights separately | Do not make blanket assumptions based on E3/E5 alone |
The new Outlook and classic Outlook are not the same
Special care is required for organizations performing business automation.Mechanisms dependent on classic Outlook, such as VBA, COM add-ins, and the legacy Outlook Object Model, may not be directly transferable to the new Outlook.Check the official Microsoft feature comparison before migrating.
For example, if you have a workflow where you save email attachments every morning using Outlook VBA, test alternative methods before switching applications. While replacement with Power Automate, Microsoft Graph, or standard rules may be possible, identical behavior is not guaranteed.
The flow from email reception to calendar reflection
sequenceDiagram
participant S as 送信者
participant E as Exchange Online
participant O as Outlook
participant U as 利用者
S->>E: メール / 会議依頼を送信
E->>E: 配信・ポリシー処理
O->>E: メールボックスを同期/参照
E-->>O: メール・予定表情報
O-->>U: 受信トレイ/予定表に表示
U->>O: 会議依頼へ応答
O->>E: 応答を反映
Understanding this diagram helps isolate whether an issue lies with the Outlook interface or the mailbox/service side during troubleshooting.
Try first: add search criteria one by one
Instead of building a complex search right away, narrow down by sender, then subject.
from:example@example.com
Next, add criteria.
from:example@example.com subject:請求
Check this area
Verify whether the number of search results decreases as intended. Because search syntax and available criteria may vary depending on the Outlook version and search environment, it is safer to test incrementally in the actual environment.
Try changing one setting
subject:請求 to another subject keyword to get a feel for which condition is narrowing down the results.
Do not start inbox rules with deletion
Start with actions that are easy to revert.
条件: 件名に「週次レポート」を含む 処理: 「週次」フォルダーへ移動
Automatic deletion, external forwarding, and auto-replies have a high impact and are not suitable for initial testing.
PowerShell: inspect files without interacting with Outlook
If you only want to check whether files such as .msg or .pst exported to the PC exist without modifying Outlook itself, you can start with read-only PowerShell processing.
$path = "$env:USERPROFILE\Documents"
Get-ChildItem -LiteralPath $path -File |
Where-Object Extension -in '.msg', '.pst' |
Select-Object Name, Extension, Length, LastWriteTime
What to inspect:Only file name, type, size, and last modified date. It does not delete, send, or modify emails.
Success criteria:If target files exist, they are displayed in a list. If none exist, nothing is displayed.
Change one location: $pathBy changing this to the folder you want to check, you can change only the target range.
Microsoft Graph: First, read your profile
Even when trying Graph, do not suddenly request email sending and deletion permissions.
Connect-MgGraph -Scopes "User.Read"
Get-MgUser -UserId (Get-MgContext).Account |
Select-Object DisplayName, UserPrincipalName, Mail
This is an entry point to verify whether you can connect to Graph and read your basic information. Reading email bodies requires different permissions, so add permissions after your objective is determined.
If you are in an environment where you can use Copilot
このメールスレッドを、 「決まったこと / 未決事項 / 私が対応すること / 相手に確認すること」 に分けて整理してください。 本文にない期限・担当者・決定事項は推測せず「未記載」としてください。
Compare the generated results with the original text. In emails, plausible auto-completions of deadlines or assignees directly lead to erroneous transmissions.
Common use cases at work
| Situation | Approach in Outlook |
|---|---|
| Department representative email | Consider using a shared mailbox rather than continuously forwarding to individuals |
| Weekly recurring notifications | Consider folder organization based on rules |
| Task management | Do not use email as the sole task log |
| Meeting coordination | Use calendars and meeting requests rather than the body text |
| Confidential information | Check organizational rules such as sensitivity labels, encryption, and DLP |
| Automated processing | Check differences between New and Classic Outlook, APIs, Power Automate, etc. |
Key points for IT departments and administrators to verify
Currently assigned Microsoft 365 / Exchange licenses
Deployment policies for New Outlook and Classic Outlook
Dependencies on existing VBA, COM add-ins, and business integrations
External automatic forwarding and mail flow rules
Shared mailboxes and delegation permissions
Anti-phishing and anti-spam measures
Relationship with retention, auditing, eDiscovery, DLP, and Information Protection
Licensing and data access scope when using Copilot
Official and primary sources
The shortcut to understanding Outlook is not just looking at inbox operations, but rathertreating it as handling business information in Exchange Online from multiple Outlook clientsOnce you grasp that, topics like search, sharing, migration, automation, and security all connect into a cohesive whole.
