If i will use an Apple product without the @icloud.com mail, i will post some usefull function other than mail offered by Apple? (That i read that is not reliable)
I'm not sure i get your question - if you are asking if you lose anything by not having an iCloud account linked to an iCloud.com address, no. And mail will still work regardless.
Even though your AppleID has an associated email address, you are not obligated to use it. You can use any email account with your Mac and iOS products.