SMTP plugnlins

Hey guys, Does anyone know if Contact forms actually have the ability to drop emails in Inbox or spam folder?

Example: I have a weird case, where from the same site we designed a form using Gravity and Divi forms.

When we tested the emails that were send from gravity lands in spam or the client says they haven't received any emails at all. While we see emails as delivered in the dashboard. Even I saw there were no trace of emails in their email address we sent from forms.

Where as divi the emails we sent, landed in inbox and I am not sure how is that possible.

Can anyone tell me why is there a difference here?