Cleaning out your database of email contacts is important when you offer an affiliate program directory. If your list of contacts is outdated, your trustworthiness in general can be called into question by your visitors. Cleaning up your contacts source can also help you steer clear of the "spammer" label when you send out your newsletter (ISPs can view someone who sends to too many dead addresses as a potential spammer). Check your mailing statistics and clean out all the hard bounces from your list.
If it's worthwhile for your business and you have physical addresses on file, consider sending a postcard to people whose email has bounced. Tell them you've recently had problems with their email address of record and ask for an updated address if they're still interested in subscribing to your list.