

The purchaser of that domain will be able to send and receive email from your addresses.
The biggest concerns here are probably:
- The new owner taking over accounts that use the old email (either via password reset or email or by contacting support).
- Sensitive personal information intended for you being sent to the new owner.
- Someone spearphishing people you know from your old email address.
The owner of the domain owns DKIM. It offers no protection against that.
The only actual protection would be PGP because it provides your key as an identity rather than the domain itself.