The candidates of the duplicate contacts are shown at starting/finishing of contact confirmation.
When the contact same to a new contact exists, you can choose to save as an individual contact or to merge to the existing contact.
On adding a relation, the different attributes between the new unconfirmed and existing confirmed contact are shown.
You can choose each different attribute to update.
You can configure the automatic detection in the system settings.
You can select the criteria of the contact duplication from name, company, email and/or mobile.
You can select contacts in contact lists or find similar contacts with name or email address to show the merger dialog.
You can merge duplicate contacts with selecting the contact and card images/attachments/tags/relations to keep.
You can select different attributes individually to merge.
Only the modification history of the kept contact remains.