I've already received an email from Chase about this. Here's an excerpt from the email:
Chase is letting our customers know that we have been informed by Epsilon, a vendor we use to send e-mails, that an unauthorized person outside Epsilon accessed files that included e-mail addresses of some Chase customers. We have a team at Epsilon investigating and we are confident that the information that was retrieved included some Chase customer e-mail addresses, but did not include any customer account or financial information. Based on everything we know, your accounts and confidential information remain secure.
According to this TechCrunch post
, other banks affected include Citi, Capital One and US Bank.