In a way I don't agree that opening new threads doesn't help. I have configured many things thanks to threads that exist.
Another thing is that the policy of CWP is that, in the face of a problem of this type, a ticket is opened and not a thread, then, there I have nothing to say because it is the policy of CWP-Studio4Host.
Surprisingly I managed to solve it, as I said at the beginning, I solved it by making a configuration that I did not like at all, I could not say the exact word in English that describes it, I am going to use a translator, so I do not know how it will be: In my language it will be I'd say "botched" but it worked.
Well, I was doing the migration tests, so just before starting the migration I had a snapshot of the VPS, they were tests because the dns in cloudflare still pointed to the old ip (except in the moments of tests that it pointed to the new one) and there I saw that problem ...
Last night, I rolled back the snapshot to make the final transfer / migration ...
Before continuing, I had the snapshot with everything configured but without any migrated accounts. SW. installed from 0, CWP installed from 0 and the necessary settings for php-fpm and php.ini.
Well, my surprise comes when, doing exactly the same as the previous time ... now yes, mail.mydomain.com now works without any problem!
I start to look for the differences, the only one, when I did tests, I renewed the SSL certificate by pressing the renew button now, this time not, as the cPanel certificate had 2 days left, shortly after finishing the migration the system automatically renewed for 90 days, I just had to add SAN for mail and webmail and .... it works! Now it works well.
Yes, between my testing and last night, there was a CWP update but ... I highly doubt it.
Maybe it was that clicking on renew now affects something? I don't think so, but it's the only thing different ...
The rest of the process, identical, first I changed dns in cloudflare pointing to the new server in the mx record and mail.mydomain.com, I saw that everything was going well and .... I already changed the rest of the dns's.
For my part there is no explanation, I do not know if when there is a transfer it is different than if we create an account of 0 in CWP, for example, if I go to Domains-List Domains none appears (and I have two active accounts-domains ), but to think something ...
For the rest, what I mentioned (and this post is long) I did the process exactly the same as the other time, except that I let the certificate renew itself and ... it worked ...
Greetings!