Email solution for static domains

Hi, I’m looking for email solutions for small clients that receive a couple emails a month through their contact form on their static website.

Currently my clients are hosted on DO (Ubuntu 16), serverpilot is the control panel, and Machform is the form builder hosted under my domain. I configured the SPF / DKIM for my domain and emails are still going to the spam folder. I’ve also tried using Cognito forms but still have issues.

Most of my clients don’t have a professional email address so what I would like is the form to send an email to their gmail address with no-reply@theirdomain.com and avoid the spam folder. I don’t know if that is possible but I’m looking for easy and affordable solutions. Thanks!!!