After I switched my NS to Cloudflare, my emails got routed to on of my old mail servers instead of the intended

hi, I am glad to join the community and I hope someday soon I can contribute and help.

yesterday I had an issue, as I attempt to gain dns control of one of my domains which is managed by 3rd party company. I have cloned all the dns records on my new Cloudflare account and changed the NS servers from the domain registrar side. strongly the emails got routed to one of my mail servers that i no longer use for this domain. so I revert back to the managing company NS records.
I am pretty sure that all the records were the exact same as intended.
and i’m wondering what could be the reason and where should I start looking.