Two emails for one person = SF confusion

I've uncovered a handful of customer accounts transitioning email domains, and contacts thus using two addresses at the moment. So bob@acme.com and bob@acmecorp.com are the same person. Due to Eloqua's unique ID being email address instead of using an ID, the system sees this as two different people.

In my case, the contacts are confusingly using both addresses, and have registered for some events on email 1 and other form fills on email 2, so the scoring is spread across two contacts. In Salesforce, they're one person with one contact ID (both emails are included on the SF contact as we do have an "other email" field in use).