The first notable characteristic is the design itself. Trial expiration emails often toggle between plain text from a team member and fully-branded HTML/CSS emails from a generic address. Abstract showcases a balanced blend between the two: just enough design to feel professional and call attention to important elements, while still maintaining a personal and conversational undertone.

It gets straight to the point: the trial has expired. An email like this, being sent after a user has not completed an important milestone, needs to be direct. Otherwise, there's a high chance it'll go unread completely. This way, the intent is known right away. The fact that the trial expired actually makes for a nice hook, grabbing the reader's attention.

Now, the major psychological tool is applied: Loss Aversion. The way their trial is designed, users *lose* access to features if they don't upgrade. This is also coupled with the Commitment & Consistency Bias because users will have likely already experienced and possibly even gotten into a habit of using the features available on upgrade.

I'm a big fan of the "implied question" which uses a statement to gently express what you want someone to do. "Let's change that" reads so much better than "Want to keep these features?"

Now my favorite part. A huge button. It's well designed, but it's also subtle since it lacks color. Instead, it's size and depth makes it impossible to miss and very clickable.

They say a picture is worth a thousand words, and a face in an email is worth a thousand clever salutations.

Finally a p.s. that includes a link to content that directly relates to the product and reminds users of the value they can get from it.