Suggestions for submission protection

[Daniel Miller]

I have what seems to be a reasonably stable and functional filter 
protecting my port 25 SMTP interface to the outside world. However, most 
filters (including postscreen) state they are not intended for use 
between MUAs and the MTA. Therefore my 587 submission port does not have 
additional filters beyond TLS & SASL AUTH.

I'm seeing some higher levels of attempted logins from various sources. 
Are there any automated filters that are suggested? Or do I simply add a 
check_client_a_access and reference a manually maintained blacklist?
--
Daniel