I will assume that matching first and last names identifies a duplicate here, but you can modify this approach to include more fields if needed.
Define a text field in your table and give it this auto-entered calculation:
First Name & " " & Last Name
Click the validations tab and specify "unique values", "Validated always".
Put this field on a layout based on your contacts table, enter browse mode and put the cursor in the field. Select Replace Field Contents and use the above calculation to update this field for all your existing records.
Now, when you import records, data with a matching combined first and last name will be excluded during the import.
I asume i can validate with email addresses? as there are a few "john smiths" in the database already
I'll give it a try and let you know
for some reason it's trying to add another 53000 contacts, I only have 12000 in there and am trying to add 93 more what could that be?
Setting up a unique values validation on the email address field should work.
I have no idea why it would be trying to add 5300 contacts. How many rows are there in your excel spreadsheet?
Sorted that out now many thanks