WordPress WooCommerce email notifications going to spam folder

I have just built a new WordPress site for a client, and repointed the domain's (mellowmarshfarm.com) DNS records to the new hosting service, Flywheel.

The client's custom email address is hosted by a different provider, and the notifications for the site are forwarded from WordPress via fw-mail.com, but they are going to the client's and customers' spam folders. I have tried adding x.fw-mail.com to the mail host's SPF record, but it didn't make a difference:

v=spf1 ip4:[redacted] include:spf.antispamcloud.com include:x.fw-mail.com +a +mx ~all

What else must I do to ensure the emails are associated with the new site and validated?