No, they can't. Or rather, they can, but they'll be wrong. The ‘+’ is not a feature of email addresses; it doesn't mean anything different from any other charac

No, they can't. Or rather, they can, but they'll be wrong. The ‘+’ is not a feature of email addresses; it doesn't mean anything different from any other character. It's just a feature of some destination systems that they ignore everything from ‘+’ when assigning incoming mail to accounts. Generally, that's configurable; e.g. in postfix it's set by the optional |recipient_delimiter|. Suppose it's set to ‘-’, and you, John Public, sign up for SuspiciousService using the email address <john+public-suspserv@example.com>. Normally, the mail gets delivered to your 'john+public' mailbox. But if Mr Spammer strips everything from ‘+’, he sends to <john@example.com>. And your system knows that that is not only not a valid local mailbox, but also that it matches a plus-stripped address, and therefore consigns the message and its sender to the fiery pits of hell.