Welcome to Shopify Community. My name is Olivia and I work here.
I really appreciate you reaching out to our network and sharing your question. I would love to help you fix this up today and help prevent emails sent from Shopify from being marked as spam. I noticed you mentioned you already have your DKIM txt records set-up for Zoho mail. Shopify uses the Sender Policy Framework (SPF), which means you would also need to add SPF records to your DNS settings. I am not sure if you already have these set-up and 'SCF' records was a typo? Just in case, let's make sure you have it added.
This will make sure none of the emails are marked as spam or bounced back from your customers. To verify your customer email address, you need to add the following SPF record to your TXT record in your custom domain settings: v=spf1 include:shops.shopify.com ~all. Doing this prevents your emails from being flagged as spam or from failing to be delivered.
I also have a really great manual here that expands on the steps above.
Voila! That should do the trick going forward, but just in case you did already add these records we want to make sure the email provider you use doesn't enforce Domain-based Message Authentication, Reporting, and Conformance (DMARC) policies. Why? This would prevent Shopify from sending emails as their domain.
To check compatibility, you can follow this great tip. Send a message from your account to
firstname.lastname@example.org and you will receive a summary of your host's authentication methods. If you see SPF check: pass in the Summary of results then your address meets Shopify's security settings.
Touch base with me and let me know if that works!