The plus sign thing works with other email providers and servers. I used to use it with self-hosted postfix and I know it's possible with exim as well. I think

The plus sign thing works with other email providers and servers. I used to use it with self-hosted postfix and I know it's possible with exim as well. I think exchange can do it as well. I would assume that any sophisticated spammer would try removing plus sign suffixes from harvested emails.