Spam folder is one of things that annoys me in email. It really doesn't make sense: if message is spam, then why store it at all? But legitimate messages silently going to spam folder is critical, unacceptable failure. You could regularly browse spam folder, but then.. what's the point? You would be skimming through all the junk anyway, that's defeating whole purpose of filtering.
Personally I don't have spam folder: either message is rejected immediately at SMTP time, or it goes straight to my inbox. (another thing that annoys me is greylisting, it just breaks instant messaging for no good reason)
Storing spam messages does make sense. If you asked me the number of times when we've sent something to someone, they told us "We haven't received anything", and we answer "Check your spam", and there it is...
Checking the spam folder is useful when you know something should be there. It's not made to skim through the junk in the hopes of finding a mislabeled email. And storage is so cheap nowadays that it doesn't make sense to not store everything to shave a few megabytes of space.
Most spam filters do silently delete messages that they are particularly confident about.
But spam detection is not black and white. The existence of "maybe" spams means that you need to let some through.
Having a separate folder is still useful because you can check it less often, and have no notifications for it. I check mine every couple of days or so. No email is so urgent that I need to see it in 24 hours.
You seem to be very convinced that there is an efficient way to filter 100% of spam without false positives. Which seems optimistic if you have ever dealt with email, text analysis or any aspect of spam detection.
Google is incredibly good at this. I see maybe 20 false negatives a year (they usually get corrected if I don't check my mail for a few hours) and 1-2 false positives. This out of thousands of good emails and 100,000+ spam mails.
That said, I think it's good to keep the "spam" folder. I normally only check it if I learn through another channel that I should have got a mail, I don't "browse it every few days" as some others suggest.
Interesting. My experience has been exactly the opposite. For me, using Gmail is like using Microsoft word in 2007. Slow interface, 34 different navigation menus, emails from friends appear in either promotions or updates at random, spam filter has a false positive once per week.
The only thing missing is the little animated paperclip guy.
Can't say I've ever had personal email end up in Promotions, but would have thought it would learn after you move a message that had landed there into your inbox...
The problem is that then it would turn into an arms race - the spammers would use that information to perform reconnaissance and learn what gets through and what doesn't.
OP is saying that any failure should propagate back as an SMTP error code, rather than lying to the sender with success while silently hiding the message. OP is not wrong - it's just not how most MTAs are currently set up.
An imperfect classification is still useful. I can focus on messages that are more likely to be important most days, and only check the spam folder once a week or so. Checking the spam folder generally requires little attention and can be scheduled for when I'm tired/distracted/whatever.
Searching the spam folder is a source of entertainment to me. Every so often I'll get an especially elaborate one, they're pretty funny to read sometimes.
Personally I don't have spam folder: either message is rejected immediately at SMTP time, or it goes straight to my inbox. (another thing that annoys me is greylisting, it just breaks instant messaging for no good reason)