Using count if in an Access Table

I have a excel sheet with years worth of entries, this contains all sales to customers, i want to move this to an access tables and eventually to SQL to integrate into a CRM.

In the excel sheets I have used this formula to tell me at input of a new sale if this an existing or new customer we use the clients domain name as the identifier so there is no issue of wrong spelling or variations

=IF(COUNTIF($A:$A;$A:A)=1;"New";"Existing") How do i do the same in access i'm stumped.