We send out mail and use the current CRM's contact ID (or as we call it an account number) and we ask them when calling in to let us know that number so we can look the up quicker.  I was told that in Zoho, in order to keep an autonumbering capabilities while adding new leads, I would have to create a custom field.  The LeadsID is not searchable in Zoho.

I was testing importing leads and the autonumber custom field I created is not shown as choice when mapping my imported data. 

So am I doing something wrong?