Another year has passed and still, email remains a stronghold among marketing channels with a high return on investment and increasing portability as the only universal app. No, email may not be as shiny as Snapchat or that cool new live feature on Facebook. Email is, however, more relevant than ever as it continues to please the C-suite by remaining a steadfast workhorse that delivers revenue and builds relationships with customers.As we close one year and embark on another, I wanted to share five of my favorite email marketing topics in 2015: 1. Open-Time Personalization Took OffWhile open-time personalization has been around for a few years, I believe it became more popular in 2015 as a viable means to present real-time content based on device, location, weather, etc. It goes beyond dynamic content and gets us one step closer to being truly contextual in our email marketing efforts. 2. Thinking Differently About MetricsMetrics are constantly on my mind, as evidenced by my columns this year. I saw potential disruptions in the email conversion funnel and shared how to think differently about clicks. You never know-a new insight might be gleaned from thinking a little bit differently about results! 3. Investment in Data and AutomationBased on countless conversations I had with clients and prospects, this year seemed to be the one where email marketers were finally gaining traction on overcoming our collective hurdle-access to data. While the inbox isn't showing fruitful results yet, I am working with more companies that have decided to make an investment in a sophisticated data ecosystems to enable smarter marketing and automation. Don't challenge marketers to come up with ways to overcome data hurdles until the ideal data structure is achieved. 4.Email Addresses were Heralded as the Digital KeyThis year, the email addresses were widely recognized as an important online identifier, because you can't set up an online account or make a purchase without one these days. Marketers truly recognized the power of email addresses with the launch of custom audiences by Facebook, and the new Google product that was released in 2015. 5. ESPs Demonstrated That They Still Have ItI'd be remiss if I didn't touch on the continued investments, acquisitions, and mergers that have happened this year in our space. It's really exciting to see companies that primarily focus on email and cross-channel marketing continue to be a viable investment in the eyes of the market. It's a great time to be an email marketer. Our heyday isn't over!As we close 2015, what are you reflecting on about email? Let me know in the comments. Cheers and Happy New Year!This article was originally published on MediaPost on January 7, 2015.