Defining unengaged subscribers for removal from email lists is a nuanced process that lacks a one-size-fits-all solution. The consensus emphasizes the importance of maintaining list hygiene to protect sender reputation and improve deliverability. A common timeframe for identifying unengaged subscribers ranges from 3 to 18 months, influenced by factors like sending frequency and target audience behavior. Key metrics include opens, clicks, website activity, bounce rates, and spam complaints. Before removing subscribers, implementing a re-engagement campaign is strongly recommended. Hard bounces should be removed immediately, and subscribers who consistently mark emails as spam should also be promptly removed. Decisions regarding the definition of 'unengaged' and subsequent removal actions should be tailored to individual business models, customer interactions, and delivery impact assessments.