Ok, update. I had problems receiving mail in Thunderbird, so I started investigating and find out that Cloudflare SSL is NO good for mail servers (my bad).
My question is:
Is there any way of automating the process in aapanel to renew the Let's Encrypt certificate in the mail server?
It is a pretty crucial issue because many times I realized the certificate was not working and emails were not being received. And this not always happen when the certificate date is past due, sometimes it happens a few days before.
For what I found in this forum there is no way to do it, but maybe somebody found a way to do it via cron or something.
Thanks!