@sandro I don’t mean to transfer the domain to Cloudflare registrar, this isn’t allowed yet for .it and I know.
But as far as I understood, they still can host my dns zone in place of my registrar. I already achieved this with some .com, now I’m in doubt the issue could be the tld, since this isn’t the only domain failing to transfer.
My tests follows, I appreciate your contribution.
img 1) The screenshot that didn’t uploaded.
More tests you could try to diagnose: https://dns-check.nic.it
img 2) configure tests as follows:
img 3 and 4) Results I’m getting indicates 184.108.40.206 (the mx record’s resolved ip) can’t be resolved:
img 5) BTW it’s not true!!
Also, .com has same mx and spf records mentioning mail1[dot]mlnz[dot]net and it smoothly migrated to Cloudflare in less than 6 hours.
Sorry if it’s not easily readable, I have limits for links and images.