I learned some new tips today regarding mobile email via Marketo’s Webinar on “The Definitive Guide to Engaging Email Marketing — Part 1: How to Grow Your List, Break the Rules, and Win.” While the speakers generally assumed that the audience was using email to market products, these tips for mobile email optimization apply to subscription content just as much as eCommerce sites.#1. Design for small screens. That means that not only should the buttons be big, but the font should be legible when viewed at 50%.#2. Be cognizant of your “pre-header” text. That’s the grey preview text seen a mobile email viewer after your from line and subject line. Many company’s waste this space with language like, “Can’t view this email? Then click here…” But using this space strategically can increase open rates, so don’t waste it on directions. Instead, include your CTA here. Even better — hyperlink it so that it’s the first thing mobile users see without scrolling.#3. Design for different devices. The most cited way to do this is to use responsive design. But the Marketo Webinar speakers disagreed, saying that an alternate option is to use a text-only email, as it’s the only design type that’s guaranteed to look good on all devices.We disagree.During an Insider Webinar last year, Justine Jordan explained why a text-only email can hinder your email marketing campaigns since hyperlinked text is harder to click on than buttons.In other words, your click-through rate will drop. But that behooves the question — what’s the goal of your email campaign. For subscription content sites, that can vary from transactional or free newsletter emails to marketing emails trying to sign up new subscribers. If you just want readers to read your email, a text-only email is the way to optimize for mobile. If you want click-throughs on mobile, having big, click-able buttons is better.Given this debate between “experts,” I’m interested what subscription content sites have found works best for them. Do you use text-only or responsive design in order to optimize your emails for mobile viewing?