Avoiding duplicates in a CRM is difficult, especially with a team of people working in the same space. Attio does a great job of automatically merging almost all duplicates, but sometimes some slip through the cracks. So we've added duplicate prevention and Contact merging.
If you're adding Contacts and an email or domain is already in use, you'll be notified and get the option to merge the duplicates. You can also merge Contacts manually, even if they don't share any information.