I tried to use MailTags, tried really hard. But it never achieved its promise. First, tagging E-mail was just too much of a hassle, second, there were bugs and

I tried to use MailTags, tried really hard. But it never achieved its promise. First, tagging E-mail was just too much of a hassle, second, there were bugs and issues and I spent a lot of time with support to try to resolve those, and third, there just wasn't that much utility, especially given the speed of Mail.app's search window on SSD drives. I stopped using MailTags and never looked back, although the remains haunt me to this day (Spotlight complains about mail header problems). I would not recommend MailTags, unless you enjoy spending time tagging your E-mail and have some spare time for support conversations.