Mail Issues (Google Domain Accounts) with OS X El Caption install. Warning!

Well, don't know who else has experienced this (or if this is a seek for help or rant), but installed El Caption. After install all my Google Mail accounts stopped functioning. I have these setup to receive as POP, and they are my own Google Apps domains (eg. dog@mydomain.org).

Anyway, after install all '@mydomain.org' accounts stopped receiving/sending mail, so thought I'd jump into Mac settings and do a simple delete account/re-add account to fix, but the bloody thing deleted all the mail in my inbox upon deletion, plus even after entering all the correct data again still doesn't work.

In connection doctor its just says that logging into POP & SMTP have failed due to incorrect username and password, which I know are correct and work fine in a web browser. I even tried to setup as IMAP but same issue. It would seem like Mac Mail has an issue with any username/password for any @mygoogledomain.org accounts, regardless if correct, so has to be some issue between Google App email accounts & Mac Mail.

Funny thing is the standard '@gmail.com' accounts don't have an issue. Arrrrg. Very annoyed El Caption, not a good start!