mail sync iCloud

I am using iCloud mail account as well as other types of accounts (Gmail, etc) and different HW (iMac, iPhone, iPad)

All mails arrive correctly on iPad and iPhone BUT on iMac i have problems syncing mails from iCloud i.e some mails do not appear or only days later in my iMac mail.

I have tried disabling the iCloud account on iMac, closing and opening iMac mail app. Creating new iCloud profile. Nothing seems to work.

It is a random problem and therefore even more annoying as i have to check my other devices to notice that some iCloud mails have been missing.

I know it is not a new problem for Apple but i wonder if a fix does exist.

Tks