Everything had been working fine before we bought a dedicated IP (on our cPanel shared-hosting package). After that, no email has been sent to Gmail accounts successfully.
When we brought it up with the hosting provider, they said you must disable Cloudflare.
And we’ve tried it many times, and actually, that fixes the problem; as soon as we change the Cloudflare proxy to “DNS only”, the emails will be sent successfully to Gmail accounts.
It’s frustrating, we’ve been digging the internet and found nothing.
I remember, cPanel sometimes doesn’t activate DKIM at all and it’s not a until it scans and figures it out on the “external DNS provider” (Cloudflare) that it’s existing one, until them it’s displayed
If it’s recognized and correct, you’d get a blue notification at the top right corner of the cPanel saying that DKIM is enabled and active, therefore on the domain list under the “Email Deliverability” you’d have near your domain name.
Maybe some time needed to process this, like 1hour or more for other MTA’s like Gmail.
Google (and many e-mail services) requires “Forward-confirmed reverse DNS”, i.e. that the IP address associated with the MX record (mail.watchmyipmonitors.live, in your case 188.8.131.52) matches the domain, but if you reverse-lookup that IP address you get watchmyipmonitors.live, which is mapped to a Cloudflare address).
If you want this to work, you should have a dedicated IP address for the e-mail server, or disable Cloudflare.