Increasingly popular is retargeting using e-mail lists (sometimes referred to as CRM retargeting). An advertiser simply uploads an e-mail list from their database to a vendor, who matches the e-mail addresses to user cookies (with varying match rates depending on the vendor). These users can then be retargeted as if they had visited the advertiser site. E-mail list retargeting is common on Facebook and Twitter, where other user credentials beyond e-mail address (such as a phone number or social network ID) can be used
