Re: How do I get data in table A that is not in table B, but by only looking at one specific column?

Power Query would be a more proper approach. Check

let  
    LeadWebsite=  Table.FromRows({{"Mrs S Smith", "1 Test Road, Test, TE5 73D", "smith@test.com"} , {"Mr Jones", "456 High Street", "789101"}}, {"Name", "Address", "Email"}),

    DataBase=Table.FromRows({{"Mrs Sandra Smith", "1 Test Road, Test, TE5 73D", "smith@test.com"} , {"Dr Jackson", "20 Roman Close", "xxx@xxx.com"}}, {"Name", "Address", "Email"}),
     
    RemovedRows  =   Table.FromList(DataBase[Email], Splitter.SplitByNothing(), {"Email"}, null, ExtraValues.Error), 

    FilteredLeadWebsite= Table.RemoveMatchingRows(LeadWebsite,Table.ToRecords(RemovedRows)  ,"Email")
in
    FilteredLeadWebsite

In the query editor window, right click on the query list panel, right click and create a blank query.

Select the created query, open the edit window and paste the power query.

Check the steps one by one