Error: 'There was a collision with an object of an incompatible type. Skipping object'. (NETIQKB38018)

fact
Exchange migrator 2.x

symptom
Error: 'There was a collision with an object of an incompatible type.  Skipping object'.

cause
This message is generated when a source custom recipient has the same smtp address as an existing target mailbox. 

fix
This is by design.  Exchange Migrator is not designed to merge a source custom recipient with a target mailbox. 

Formerly known as NETIQKB38018