Step 1: Adjust your auto-dedupe settings
  1. Navigate to Control > Administration > Organization Setup > View/Edit Org Info
  2. Scroll to the bottom and choose Edit
  3. Under auto dedupe setting choose Merge if Email matches exactly
  4. Select Save
Step 2: Upload your .csv file
  1. Navigate to Contacts > Manage Contacts > Import Contacts
  2. Select New Import Batch
  3. Select Browse and upload your .csv file
  4. Select Next
  5. Scroll to the bottom and enter a Special Flag
  6. Select Next
  7. Select Next
  8. Select Next
  9. Map the email field
  10. Select Import Now

You will now be able to query on that special flag, when you create your receiver query use contacts > profile > personal info > other > special flag
Select add and enter your special flag