Q: mac mail not working

Connection Doctor showed my six email accounts succeeded in being connected, although the Yahoo account takes over a minute to do so.  Yet, when I check my Mac mail application, I'm unable to access the account.   

I'm grateful for your offering to help.  Although I'd tried everything I could think of to correct my situation where there's an exclamation mark next to my Yahoo Mail account, I got nowhere despite restarting my Macbook Pro, checking with Connection Doctor, etc.  Something was suspiciously amiss, as Connection Doctor took much, much longer to connect than with my other email accounts (Gmail, Comcast, Hotmail).  But inexplicably, as I'm trying to retrace the paths you'd offered, everything seemed to have corrected itself, as I now, for the first time this morning, see the exclamation mark next to my Yahoo account disappear with access to my Yahoo mail.  THANKS!