Even if they could reuse a DKIM hash on an email (pretty sure this is unique per email and would fail on a legitimate check), SPF would show its obviously not from Google. So just make sure your email server correctly handles DKIM verification and blocks SPF hard fails, and you’re probably good against this.
SPF won’t help here because the attack specifically uses legitimate sending infrastructure - they’re forwarding through a compromised Google Workspace account so the SPF check passes, while reusing a valid DKIM signature from a diferent message.
Even if they could reuse a DKIM hash on an email (pretty sure this is unique per email and would fail on a legitimate check), SPF would show its obviously not from Google. So just make sure your email server correctly handles DKIM verification and blocks SPF hard fails, and you’re probably good against this.
SPF won’t help here because the attack specifically uses legitimate sending infrastructure - they’re forwarding through a compromised Google Workspace account so the SPF check passes, while reusing a valid DKIM signature from a diferent message.