Event ID - 8286

Event Id8286
DescriptionADC will not replicate from <object name> to <object name> because the source object is a CustomRecipient but the target object is a mailbox. If this is a problem, considermaking the Connection Agreement an Inter-Organizational Connection Agreement.<connection agreement name>
Event InformationAccording to Microsoft:
This event indicates that the source object in the description section is being replicated to a target object that is already mailbox-enabled. This can occur for several reasons depending on your Active Directory environment. If a target object has already been mailbox-enabled, this linking is not possible.
Ensure that the target object you want the source object to replicate to does not have any mail attributes stamped on it. If necessary, remove the mail attributes stamped on the target object. Be careful when you remove mail attributes because if you remove the mail attributes from a valid user object (one that may have already been matched), that user may be unable to access their mailbox.
Reference LinksExchange (MSExchangeADDXA)

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