Is there an email module similar to the search, just to allow a visitor to enter email address to receive promotions?
There are few modules for handling email campaigns, like Simplenews and Newsletter. But these modules are huge and don't have only subscription form. They provide whole system for working with lists, newsletters etc.
If you need only subscription form, try Webform module and create one webform node with email component. You have check box to configure this node as block.
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