Mail delivery incomplete for gmail

I have email forwarders setup in cpanel (mail server) to forward my domain email addresses (ex. [email protected]) to another gmail/gsuite managed domain (ex. [email protected]) and I’m getting errors when attempting to send emails from a gmail account (ex. [email protected]) to any domain.com email addresses. However emails from other domains (ex. hotmail, yahoo) successfully send to domain.com email accounts. After several hours or even days I’ll receive the bounce back email error message:

Delivery incomplete
There was a temporary problem delivering your message to [email protected] . Gmail will retry for 21 more hours. You’ll be notified if the delivery fails permanently.

Our DNS is managed through Cloudflare as well as our MX records. I’ve had cpanel support point to this being the issue, however we’ve had this setup for years and this only started happening within the last few months.

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Hi @mbourne,

Are you sending the email through Gmail’s SMTP servers or through cPanel’s? Do you have access to webmail through cPanel to test if sending works from there?

mail is going through cPanel’s SMTP server and yes I have checked webmail and emails are working when sent through webmail.