I've been thinking about how email list quality changes over time, even when people originally signed up themselves. Some addresses become inactive, while others start bouncing after working fine for months. Removing contacts too aggressively can also mean losing subscribers who may still want to hear from you.

For regular opt-in campaigns, how do you decide when an address should be removed? Do you mainly look at bounce history, engagement or a combination of signals? I'm interested in practical approaches that help maintain list quality without unnecessarily removing genuine subscribers.