I have a question along the same lines.
Emails coming to us from firstname.lastname@example.org (from our form) go into the inbox, but emails coming from the client's email address, but from our website form, go to the junk box. I have email set up to come FROM the person filling out the form with the email they provide. Does the DKIM / SPF not apply in this case even though it is being sent to us, through our hosting server. I think the answer is that they have to come from @ourwebsite.com, but just wanted to see if you can shed more light or if there is a way to make it work. Thanks.