If I have understood this correctly you have two tables that are not connected at all - ie you don’t have a record of which email connects to which opportunity.
On that basis - you need to find some rule to be able to connect them together - in other words a field in common
Do both tables have an ‘account’ field for example
If so create a third table called accounts
Create a list of account records by copying the full list of accounts from both tables into this new table and then de duping -
Then for each of the opportunities and contacts tables change the accounts field type from text to linked record and link to the new accounts table - and bingo your base is now a relational database …
If you don’t want to maintain a separate accounts table (common with a CRM) then there will be a couple of more steps to this which involve creating a look up field and then changing field types to make this connection happen
If the field in common is “email”- I would advise you not to have a separate email table - but to temporarily make the email the name field in the contacts base then change the opportunities field with email to a linked record field to connect the two tables and then you can switch the fields in contacts back.
