Using XL help file, I'd recommend looking at the MATCH formula.
For an example, I'll assume your old data is on Sheet1, new list is on Sheet2
You could setup an extra column next to your new data (Column B?). Enter
this formula in B2 and copy down.

=IF(ISERROR(MATCH(A2,'Sheet1'!$A$2:$A$1000,0)),"Un ique","Duplicate")

You could then us AutoFilter (Data-Filter) To show only the unique entries
and then copy those to your mailing list.
--
Best Regards,

Luke M
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"BlindShelter" wrote:

I have a mailing list that is in EXCEL. Occasionally we purchase mailing
lists to solicit new clients and we want to delete the duplicates from the
new lists that are already in our database. My knowledge of EXCEL is very
rudimentary so please be gentle.