I have never really understood the true meaning or usage of the term "passive aggressive".

Is this email passive aggressive? Or just a bit sad?

@AlexDeLarge indeed I feel bad for them and almost click the button.

Actually that's quite nice feature, I'd prefer more companies do the same - idle user? Stop spamming

The big question is, how do they know? Embedded tracking links in HTML mails? Internal "feature" of Thunderbird (if you use Thunderbird)?

But no matter how, it's not what I would expect from a company that wants "An Internet that truly puts people first, where individuals can shape their own experience and are empowered, safe and independent."