The following email subscription widgets for Tumblr allow to build email lists, which can be used to keep your visitors updated every a certain period of time through email. Some of these forms work through RSS, but are pretty limited when configuring the publishing options through email, other a much sofisticated and used by thousands of marketers around the web.
Before you start, make sure you don’t “spam” your tumblr sucscribers every single day, if you do this, they will end up unsubscribing for sure. Try to send email updates just once a Week, or every 15 days.
Do not mistake an email subscription widget for a contact form, the latter just works pretty much the same as your ask page and sends you the message to the email address you just added.