If you are running Mojave you need to install our new MailSuite app to get MailTags functionality. With Mojave, we have consolidated our 4 plugins into a single product with a single installer. You do not have to install all components of MailSuite if you only want to use MailTags but you do have to do the installation through the MailSuite app.
The new Great Equalizer is the SEND button.
In Memory Of Harv: Those who can make you believe absurdities can make you commit atrocities. ~Voltaire