An e-mail address can have multiple @ also for... source routing. Of course it doesn't make any sense nowadays, but it's technically allowed. RFC 5321 gives an example:
@hosta.int,@jkl.org:userc@d.bar.org
This is a valid e-mail address, with source-routing along two intermediate servers. I guess no sane server on the Internet will accept this, but you never know... (this said, I remember attempting this around 1996, when many servers were open relays, and the message was happily delivered after passing through 3-4 servers).
