My iMac won't Accept My AOL Account and Gmail Account

For some reason my iMac won't accept new emails from my AOL and Gmail accounts which was weird since it was able to yesterday. I read from one of the post on the Apple community threads that I could delete the accounts on the Account section in Preferences and just reenter them which I tried to do but I can't reenter the AOL account because it's saying it can't "verify" the account/password (And I know that I didn't put down the wrong password) and it'll accept the Google account but it won't accept the Gmail part.

Now I have a Mail app on my iMac that won't accept my AOL or Gmail accounts and I don't know what to do. So far my iPhone doesn't have a problem with reading emails and I can still look at the emails through the websites but I want to be able to use the Mail app)