We have serious problems with customers who try to submit requests with perfectly valid email addresses. It looks like addresses in .info domains are not recognized, and neither are those which use a Postfix-style ‘+’ delimiter (e.g. email@example.com). No updates are mailed out on requests with such email addresses, either.
I suggest you take a good look at how email addresses are recognized, as there may be a lot of similar problems with other domains. The feature that turns URLs into clickable links is plagued by similar problems, but it’s not a mission critical thing for us.