Resolve iCloud Email Delivery Issue

I’m running all outgoing correspondence—newsletters, booking confirmations, and day-to-day replies—through my studio’s sending software, which is tied to a Gmail commercial-grade account. Everything reaches its destination except messages addressed to @icloud.com users; Apple rejects them outright before they hit the inbox or spam folder.

I need someone to trace and eliminate whatever is triggering iCloud’s refusal. That likely means checking SPF, DKIM, and DMARC records, evaluating the sending reputation of the Gmail relay, and fine-tuning any headers or content flags that could be causing Apple’s filters to bounce the mail. If rate limits or SMTP errors are involved, I’ll need clear guidance on throttling and retry logic inside the application as well.

Deliverables
• Diagnosis report outlining the exact rejection reason(s) from iCloud
• Updated DNS records (or verified existing ones) for SPF, DKIM, DMARC
• Any Gmail-side or application-level configuration changes required
• Proof of successful delivery to multiple @icloud.com test addresses

Acceptance criteria: confirmations land in an active iCloud inbox without warnings, and the final report documents all changes so I can maintain them long term.

I can share the return messages we get when sending to icloud.com when asked