Not really surprising: in the eyes of a naive regex for extracting email addresses from a string, a+b@c.d contains a nicely email-looking substring b@c.d but a@

Not really surprising: in the eyes of a naive regex for extracting email addresses from a string, a+b@c.d contains a nicely email-looking substring b@c.d but a@c.d isn't contained at all. Spammer address supply chains aren't usually characterized by the highest levels of sophistication.