Default Organizer Mailbox

The Default organizer mailbox is a required setting for the EMS for Outlook M365 web add-in. It specifies an Exchange mailbox that EMS uses to automatically populate the attendee field for events created in Outlook through the add-in.

This setting enables drag-and-drop rescheduling in Outlook. When a user moves a synced event to a new date or time, Outlook sends a meeting update notification. EMS uses that notification to detect the change and sync it to the corresponding EMS reservation.

EMS requires at least one attendee on an Outlook event. With the Default organizer mailbox configured, EMS adds a valid Exchange email address as the attendee when the user doesn’t add one.

If you don't configure a Default organizer mailbox, EMS still creates the reservation and adds the EMS System attendee to the Outlook event. This EMS System attendee doesn’t correspond to a valid email address. After you send the event, Outlook sends a nondelivery report (NDR) because the message can’t be delivered.

The Default organizer mailbox ensures that each event always includes an attendee, even if the user doesn’t add one. This allows EMS to:

  • detect when a user reschedules an event to a new date or time.

  • sync the updated date and time to the corresponding EMS reservation.

  • maintain two-way synchronization between Outlook and EMS.

Prerequisites

Before you configure this setting, make sure that:

  • EMS Platform Services is installed and accessible.

  • You have administrator access to the EMS Platform Services Admin page.

  • You use a valid, active Exchange mailbox in your organization’s tenant.

  • The mailbox has permission to receive meeting invitations.

Configure Default organizer mailbox

  1. Open a web browser and go to the EMS Platform Services Admin page.

    Example: https://[yourserver]/platform/admin

  2. Sign in with an account that has Web administrator role assigned in Everyday user security template.

  3. Go to Calendaring > Two-way sync configuration.

  4. Find the Default organizer mailbox field.

  5. Enter the email address of the Exchange mailbox that you want to use as the default attendee.

    Use a shared or service mailbox dedicated to EMS, such as [email protected].

  6. Select Save two-way sync configuration.

After you configure this setting:

  • When you create a reservation through the M365 Web Add-In without attendees, EMS adds the Default organizer mailbox as an attendee on the Outlook event.

  • When you add a different attendee, the system removes the Default organizer mailbox.

Mailbox setup

For best results, we recommend using a dedicated shared mailbox that:

  • Is not actively monitored by end users, which helps avoid confusion from meeting notifications.

  • Has a clear, descriptive name that reflects its purpose, such as [email protected] or [email protected].

  • Allows conflicts so that overlapping meeting invitations do not create booking errors in Exchange.

Don't use a personal mailbox. A shared or service mailbox ensures consistent behavior even when personnel changes occur.

Exchange Online throttling

Microsoft Exchange Online - Microsoft 365 limits each mailbox to 30 sent messages per minute. When a mailbox exceeds this limit, Exchange temporarily throttles outgoing messages instead of blocking the mailbox.

This can cause short delays or temporary error codes while Exchange queues and sends messages in subsequent minutes. Consider this behavior when you estimate reservation volume for your organization.