It appears the attacks have mostly subsided. A large number of failed smtp attempts were blocking legit users from making connections to the mail server. The primary country that was doing this came from Bulgaria. I have blocked the entire country in the firewall. If you have clients or people you correspond with in Bulgaria, they will need to communicate some other way.
Here's a list of 'hits' to the logs from a few of the IP addresses:
root@mail [/var/log]# fgrep -c 87.246.7.229 exim_mainlog
27613
root@mail [/var/log]# fgrep -c 212.70.149.57 exim_mainlog
49473
root@mail [/var/log]# fgrep -c 212.70.149.89 exim_mainlog
31204
root@mail [/var/log]# fgrep -c 87.246.7.246 exim_mainlog
94266
The bold numbers are the number of times that IP address had attempted to 'authenticate'. These repeated authentications caused problems for everyone. I will continue to monitor it, but it most appears to be over. Let me know if you continue to have issues.