It’s ironic and kind of galling, that this HubSpot blog article refers to tagging despite it not being a feature on HubSpot:
https://blog.hubspot.com/blog/tabid/6307/bid/26404/4-tips-to-keep-your-email-list-squeaky-clean.aspx?utm_campaign=Marketing%20Blog%20-%20Daily%20Emails&utm_medium=email&utm_content=178256983&utm_source=hs_email