Several months ago, Facebook started telling the developer community it would probably deprecate its notification email feature, though it never gave a specific date as to when or how that was going happen. Then, a couple weeks ago, Facebook created a new mechanism for apps to send email to users, notifications.sendEmail – though the new method included a 1 email/user/day limit. This week, Facebook announced that that limit has now been upped to 5 emails/user/day.
It will be interesting to see how the developer community uses email in relation to messaging, feeds, and traditional notifications, and how strict/transparent Facebook will be regarding appropriate levels of application email. So far, apps have made sparing use of email in comparison to on Facebook channels, which usually convert very well.