I use tags as supplementary keywords. If you know what thread you're looking for, search is good enough. If you communicate with distinct groups of people abou

I use tags as supplementary keywords. If you know what thread you're looking for, search is good enough. If you communicate with distinct groups of people about different projects, search is good enough. If emails from the same few people can concern different projects, and there are no terms that always appear in those message to differentiate (or your colleagues are bad at using the subject line), tagging your messages with the proper project/issue/topic goes a long way. This means that any tag applied by a filter is usually pretty useless, you can just repeat the filter's query when needed.