Sync Contact in Outlook to Zoho Email ( don't use export file )

Sync Contact in Outlook to Zoho Email ( don't use export file )

Hi There, I have a problem , please help me
I have a lot of contact in outlook and now i use Zoho mail. But my customer don't want sync contact by export file and import to Zoho. so Could you share me some way to sync contact and don't use export file. Thanks