Form to email outlook could not verify identity of sender

Form to email outlook could not verify identity of sender.
form working - however test email live results in above message in outlook
anyone have a workaround

verify

Outlook requires SPF or DKIM authentication to validate the user.

So you should setup at least SPF for your domain.

DKIM is more resource intensive as it needs to sign every message.

Thanks we added the IP to our SPF record - will try that