Scan existing Comments for spam / spam protection

Hey guys,

I am searching for a solution to automatically scan all comments (needing modeartion + already approved) for spam. We are talking about 100.000 old comments which have to be scanned.

Right now I found two possible solutions:

- Akismet
Here I read that it's not possible to scan approved comments: http://wordpress.org/support/topic/rescan-old-approved-comments-with-akismet
-> which could be maybe be solved by unaproving all comments and then rescan them?

- Typepad Antispam
I couldn't find any hints of this being stil actual, the wordpress plugins seems to be working for "2.5"
http://wordpress.org/extend/plugins/typepad-antispam/

- http://wordpress.org/extend/plugins/chronological-spam-removal/
-> I am not sure if this is using an algorhythm that makes sense? but it seems to scan all comments on a chronical base...

Summary:
- Can anyone give feedback about one of my solutions or can you recommend another way?
- are there any ideas besided using the Anti Spam Pack from WPMUDEV (which is now installed on the blog), for general anti spam prevention.

Thanks for your help and apologizing for the not too well scructured post :wink:

Oli