[exim] Is this local part valid?

I've noticed quite a few emails coming in to my users with weird local
parts, and was wondering if they were valid and if email programs should
handle them fine (Exim is, but another program we also use is deffering when
it sees them). Here's an example:

MAIL FROM:<"info@???>

I'm assuming that if it is legal, it's because the email address in double
quotes is just that - quoted. Has anyone else been having issues due to
encountering emails with these addresses in them?

Eli.