Tell me which mail known as junk or spam and why some mails go to spam but they aren't spam.thanks

Junk mail is like the mail you throw away from your regular mail -- Bulk mail

When you go to a site and they ask for your email address, you get on a list

People make money selling lists -- surveys target you to receive spam...

The reason some emails are filtered out is that your email is set up to protect

You and thinks any email you haven't approved of is spam and shoots it down

That is why some emailers ask you to verify that you approved their emails...