high sierra Mail

I have 2 mac pro's 1 MacBook pro and 1 iMac, that are used daily, 1 Mac pro, MacBook pro, and IMac have been upgraded to High Sierra and the other Mac Pro still on El Capitan. The Mac pro with El Cap is able to receive and send Apple Mail, however the machines with High Sierra after trying on a daily basis for the past 6 weeks following all apples passwords instructions and checking and making sure password (according to hidden passwords on keychain) are correct I STILL can not get apple mail to work. I know according to searching on line I am not the only one with this problem. So Please Apple fix this