"550 5.1.11 RESOLVER.ADR.ExRecipNotFound" when delegate sends update to meeting after manager moved to Office 365 hybrid environment

Symptoms

Consider the following scenario:

  • A manager, who has a delegate, has their mailbox moved to Microsoft Office 365.
  • The delegate's mailbox remains in on-premises environment.
  • The manager creates a meeting on their calendar after the mailbox is migrated.
  • The delegate updates the meeting time and sends an updated version of the meeting to the invitees.

In this scenario, the delegate receives a non-delivery report that includes the following IMCEAEX address and error message:

IMCEAEX-_o=ExchangeLabs_ou=Exchange+20Administrative+20Group+20+28FYDIBOHF23SPDLT+29_cn=Recipients_cn=SystemMailbox-john@mgd.contoso.com

Remote Server returned '550 5.1.11 RESOLVER.ADR.ExRecipNotFound; Recipient not found by Exchange Legacy encapsulated email address lookup'

Cause

The legacyExchangeDN attribute value of the invitee's cloud object is stored in the calendar item. If the Azure Active Directory Connect (AAD Connect) Exchange hybrid deployment settings are not enabled, the legacyExchangeDN attribute values in the cloud are not written back to the on-premises.

Resolution

To resolve this issue, enable the Exchange hybrid deployment settings in AAD Connect. For more information, see Exchange hybrid writeback.