[__david__]

> Many spammers use lists from dubious sources and a big number of addresses are invalid. So, if they get an "unsubscribe", they know which addresses are better and can deliver more spam to it ...

That's only true of the dubious "viagra" style spam, where they got your name from a list. I don't think those even bother with "unsubscribe" links any more. I only see unsubscribe links from places where I've had to give my email up to buy something or sign up to a site. Those are generally legit and most of the techy/startup web sites will unsubscribe you immediately.

The next tier are the sites that unsubscribe you but take more than a week and will keep spamming their dumb newsletter in the meantime.

The final ones are either broken by stupidity (it's amazing how many web developers cannot grasp that "+" is a legit email character), or willfulness and will keep spamming no matter what. I block these at the SMTP level with 503 messages (usually containing some personal insults and swearing) as soon as they "RCPT TO" the unique email address I gave them.

[PythonicAlpha]

Luckily I managed to block much of the spam I got before, so I don't see the current spam behavior. But some years ago, there well existed some non-viagra style spammers that just put dubious unsubscribe links inside. I never tried myself, but was warned that they use the information against you. I would guess, that verified eMails have a greater value ... but it also might be negligible now, since with bot-networks spammers don't need to care if they send 1 billion or 10 billion eMails ...