If you use webmail on a regular basis, then you can set much lower threshold values. Very low values make a pretty aggressive filter and it is very likely that good mail will be quarantined, but that's intentional.
The trick then is to check the quarantine routinely, and the good mails that are falsely caught indicate to you how you should fine-tune your whitelist. Consider whitelisting entire domains like "@dreamhost.com".
I actually don't even use "Tag" but only "Quarantine" (I have both values set to 1). There's not much point in tagging if you're going to check the quarantine regularly anyway.
I would recommend this:
1) Set How long should mail stay in the quarantine before being automatically removed? to 30 days. This gives you ample time to detect any mails that were falsely caught.
2) Set Tag level = 1
3) Set Quarantine level = 1
The filter is not "smart" in that way. It will keep on tagging and never learn from it - but you can use the tagged messages to finetune your blacklist, if you can detect a pattern. But really, I'd recommend the above approach instead. Yes, it's a little more trouble to check the quarantine list, but you'll need to do that anyway, and the tags are just ugly in your mailbox when they're applied to legit mails.
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