Microsoft 365 mailbox

Include Microsoft 365 mailbox

In onOffice enterprise, you can integrate Microsoft 365 mailboxes using the official Microsoft Graph interface. This means that your emails are available to you in both onOffice enterprise and the onOffice app .

Requirements & Preparation

Before you begin setting up onOffice, please make sure the following requirements are met:

User Permissions in onOffice: To set this up, you need administrative permissions for the basic settings (Extras → Einstellungen → Grundeinstellungen → E-Mail). If necessary, contact your internal onOffice administrator.
Permissions in a Microsoft 365 account:
- For custom domains (e.g., company domains, not directly @outlook.de / @outlook.com), access by third-party applications via Microsoft Graph may need to be enabled in the Microsoft 365 Admin Center.
- Microsoft Shared Mailboxes: These must first be set up and enabled by your Microsoft 365 administrator in Exchange Administration.
- For any settings outside of onOffice, contact your Microsoft 365 / Exchange administrator or consult the official Microsoft Support and Help page.

Step 1: Create a mailbox in onOffice

The initial setup is performed in the basic settings of onOffice enterprise:

From the menu bar, open:

Extras → Einstellungen → Grundeinstellungen → E-Mail
Go to the External IMAP Mailboxestab.
In the IMAP Import section, under Email Address , enter the full email address of the desired Microsoft 365 account.
Click the Import Office 365button.
The mailbox will now be added to the list. Next, assign the desired onOffice users to the mailbox.

Step 2: Authentication & Authorizing Access

After creating the mailbox, you must link it to Microsoft once:

In onOffice, go to the Emailmodule.
In the folder or mailbox list, click the newly created Microsoft 365 mailbox.
The first time you open it, the Microsoft sign-in window appears.
Sign in with your Microsoft account credentials and confirm that you are granting access to the onOffice enterprise interface. (Depending on your organization’s security policy, two-factor authentication (2FA/MFA) via an authenticator app, SMS, or code may be required here.)

Important Safety Notice:

After successful authentication, all users assigned in onOffice have full access to the email content in this mailbox—even if those users do not have their own Microsoft 365 account.

Special Features & Important Notes

Synchronization and Folder Structure

When using multiple email programs at the same time (e.g., Outlook and onOffice), discrepancies may occur in folder names or the read status of messages.

Items Sent: By default, Microsoft 365 uses the “Sent Items” folder (onOffice internal: “Sent properties”).

Posting Activities from External Emails

Emails that you send directly through Outlook are automatically created in onOffice as an activity of the type Email – Outgoing (Characteristic: “External Email Dispatch”) is recorded.

The assigned primary user of the mailbox is automatically entered as the supervisor (indicated by the crown icon under Grundeinstellungen → E-Mail when mail logging is active)
If necessary, you can disable the synchronization of external emails under:
Extras → Einstellungen → Grundeinstellungen → E-Mail → Reiter: externe IMAP Postfächer.

Microsoft’s Upload and Size Limits

Microsoft 365 is subject to restrictive policies regarding the number of recipients and attachment sizes:

Microsoft may block the sending of bulk emails as well as emails to more than 10 recipients with file attachments at the server level.
Recommendation: For large attachments, use the onOffice macros _downloadLink(Text) or _agreementLink. This makes files available as a secure download link (download validity: 14 days), which reliably prevents transmission interruptions.

Set Up Alias Mailboxes

You can also integrate Microsoft 365 alias addresses into onOffice. Creating a folder in onOffice is done in the same way as creating a regular mailbox (see Step 1).

Requirements at Microsoft:

To send emails using an alias address, the “Send as Alias” (Send from Alias) feature must be enabled in your Microsoft 365 organization.

This setting is not included in onOffice enterprise.

Please contact your Microsoft 365 / Exchange administratorto enable this option in the Microsoft 365 Admin Center (under Message Flow Settings) or via Exchange Online PowerShell.

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