It seems Twitter is planning to release a tool to make it easier for advertisers to find their customers on Twitter. Advertisers will be able to bring in emails from their clients into twitter and will be able to run ads that will be served specifically to this audience. Facebook has had this tool available since 2012.
As a marketer I think this is a wonderful development. If my clients are spending a good amount of their time on Facebook or twitter, it is a wonderful opportunity for me to reach them via these additional channels. Now as a user of these channels I have a completely different perspective. First of all, when I give a company my email or my phone number I don’t expect they will be using it to target me on the social networks via ads. Second of all, companies are currently using these emails to spam their clients with the next 10% or 50% or whatever discount they may think of. If they feel this will be an extension of those efforts they will not be successful. Advertisers will have to ensure that what they are promoting is not their business, or the next sale, but valuable content. I would personally find it inconvenient to start getting in my newsfeed or twitterfeed information about the next 10% sale.
If you are creating social ads using custom audiences on Facebook now, or if you have plans to use custom audiences on twitter when it is released, keep in mind that traditional “email” content may not be what your users on these channels want. You will have to put focus on the content your audience values and test what messaging truly works.