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by curious_curios 674 days ago
Everything after the plus is considered a sub address and is just an arbitrary tag. You can include any text there and it’ll get delivered to the primary address. It’s useful for filtering emails, and is part of the email spec.
1 comments

However, a lot of websites aren't programmed to the full spec. I've seen many sites reject the use of '+' on the left side.
Some web sites don't want you create accounts like

  me+1@gmail.com
  me+2@gmail.com
  me+3@gmail.com
when it comes to making an army of sock puppets the biggest hassle is usually doing the email verification for all the accounts. The "+" trick greatly simplifies this though if somebody is looking for trouble they sure will find it. Of course if you control your own domain you can use a wildcard but if you add 1000 users to a site from the same domain that is obvious too.