How do you opt-in an existing email list? By Tim Karpisek on 6 June 2011 in Email Marketing, Opt-in, Tips, Lists Many companies have gathered an extensive contact list over the years. However, many of those contacts never subscribed to the company’s newsletter. Other companies have built up a strong set of data and have now decided to start with email marketing. In both cases, there are effective methods to hook up those contacts with your email marketing program.