Email Marketing Trends Shaping 2021
The developments that mattered for email marketers in 2021, led by Apple's Mail Privacy Protection announcement and what it meant for open-rate tracking.
Most years in email marketing bring incremental change: a new template style, a slightly better tool, a trend in subject line phrasing. 2021 brought something bigger: a change from Apple that forced marketers to rethink one of the metrics they’d relied on for two decades.
Apple’s Mail Privacy Protection changed what “open rate” means
At WWDC in June 2021, Apple announced Mail Privacy Protection, a feature built into Apple Mail that would pre-load remote content, including the tracking pixels email platforms use to record opens, regardless of whether a subscriber opened the message. Rolling out with iOS 15 later that year, it meant that for any subscriber using Apple Mail with the feature enabled, an “open” no longer reliably indicated a person looked at the email.
Given how much of the market reads email on an iPhone or through Apple Mail on a Mac, this wasn’t a minor asterisk. It broke A/B tests built around open rate, made subject-line testing less trustworthy and forced list-cleaning processes that used “hasn’t opened in 90 days” as a signal to find a new basis for that judgment. The teams that adjusted fastest shifted their primary success metrics toward clicks, conversions and revenue per send, numbers Apple’s change couldn’t distort.
Deliverability got harder to game and easier to earn honestly
With open rate no longer a clean signal, inbox providers leaned more heavily on engagement signals they could still measure reliably: clicks, replies and how often a subscriber marked mail as spam versus kept engaging with it over time. Practically, this rewarded senders who kept their lists engaged and penalized the older habit of mailing a stale list to inflate volume.
Interactive and AMP-powered emails saw a real, if narrow, push
A handful of larger brands experimented with AMP for Email, letting subscribers do things like fill out a form, browse a product carousel or RSVP without leaving the inbox. Adoption stayed limited, mostly to companies with the engineering resources to build and maintain it, but it signaled a direction: email was being asked to do more than just link out to a landing page.
Dark mode forced a design rethink
As dark mode adoption spread across mobile operating systems and email clients through 2021, marketers who’d only ever designed for a white background found their carefully chosen colors and transparent-background logos rendering badly or invisibly for a growing share of subscribers. Testing every send in both light and dark mode became a standard, if annoying, addition to the pre-send checklist.
SMS became email’s most common companion channel, not its replacement
Rather than displacing email, SMS marketing grew alongside it in 2021, generally reserved for the most time-sensitive messages while email carried the bulk of storytelling, offers and lifecycle content. The brands that got the mix right treated the two channels as complementary, not competing, with SMS opt-in built as its own deliberate step rather than bundled quietly into an email signup.
What this meant heading into the rest of the year
Taken together, 2021’s trends pointed in one direction: away from vanity metrics and toward outcomes that were harder to obscure. Open rate stopped being trustworthy, so the businesses that adapted fastest built their reporting, their testing and their list hygiene around clicks and revenue instead. That shift outlasted the year it started in, and the habits it forced turned out to be better practice regardless of what any single platform changed next.
