Glossary
DKIM (DomainKeys Identified Mail)
A digital signature added to emails that proves they were sent by a domain and weren't altered on the way.
With DKIM, the sending server signs each email with a secret key, and publishes the matching public key in its domain's DNS. The receiving provider checks the signature: if it's valid, the message really comes from that domain and wasn't modified in transit. An invalid signature is a strong warning sign.
A valid DKIM signature proves who sent the email, not that it's harmless: scammers can sign emails from domains they own. Fishi combines DKIM with other checks. Forward a suspicious email to check@fishi.email.