I, too, constantly have this issue. I'm wondering if anyone has come up with a solution.
I have a feeling it's because the subject line says, "Form Submission - Contact" and I'm wondering if that's what triggers spam filters. Has anyone tried just changing the subject line on reply? Any luck?
Is there a way to change the subject line on Squarespace side? I assume that there's nothing in the header of the contact email that would trigger spam filters - but is that possible? I don't know how to read a header - but I imagine that whatever comes from Squarespace could embed something that spam filters don't like...
Just some ideas to help us get this figured out. I have lost clients because of this as well.
Johnny B