Case Study: A/B Test Transactional Email For an 8.6% Conversion Lift

sendwithus unlocks potential for testing that is largely ignored by the marketing industry.

– Christian Croft, co-founder of uSell

Online marketplace uSell achieves 24.5% increase in open rate and 8.6% increase in revenue-generating offline conversions through sendwithus transactional email A/B testing.


We love our friends at uSell, a marketplace company that makes it easy for their customers to sell their used gadgets, by connecting them with hundreds of professional buyers so that they can get the best offers.  They are excited about transforming the way people change up their technology, and they believe in giving their customers the best user experience. Since they empower their customers to sell their old things, they are also encouraging good for the environment while enabling their customers to use the cash to buy new sweet things. We at sendwithus love what they do, and found their transactional emails quite interesting.

They described their “retention email campaign”. This drip campaign occurs once a user signs up to sell a device and a prepaid shipping kit is mailed to the customer to complete the transaction. These emails gently encourage customers to send in their devices (free of charge) in order to drive sales to the professional buyers on uSell.

The Challenge

uSell wanted to focus on their ‘send-in’ rate, this specific metric measured how many devices were sent back to uSell after customers received the shipping kit. Since uSell’s revenue depends on customers sending in their devices, they wanted to optimize the call to action in their “retention email campaign” to nudge customers to finish their sale and get paid. As the retentional drip campaign was the only source of communication with customers after they had left the site, it was critical to ensure the emails were clear. Customers had already agreed to sell a device and likely left their shipping package on their kitchen table.  How could they effectively remind their customer to take action?


Increase send-in rate

The Hypothesis:

A/B testing a variety of subject lines will increase send-in rate.

What is Email Subject Line Testing

Marketers concentrate on email open and click rates as an indication of how many people view or open an email either sent by marketing teams or triggered through developer code.  We at sendwithus encourage customer-focused teams (typically marketers) to take a closer look at their open and click rates and consider using granular analytics to better understand how their email is performing.


If your open rate is high, but click rate is low, it is likely that the content in your email body is not encouraging your customers to take action. Maybe there is too much text and not enough direction for the customer.  If your click rate is high, but your open rate is low, you could benefit from looking at your subject line.  Similarly, if your open and click rate is low, you could definitely improve your subject, body and include a call-to-action (CTA) to increase customer engagement.

With a high click rate, but low open rate in a transactional email, it would be beneficial to consider subject line optimization with A/B and multivariate testing.

The Test

uSell noted that their retention email campaign was critical to their send-in rate, and contained opportunities for optimization. They decided to try two separate A/B tests that compared the performance of three separate variants.

In their first test, they noted the winning email line, “Your old device is saying, only 1 week left” not only had a 24.5% open rate improvement, but those users also had a 7.5% increase in send-in rate.

Their second A/B test concluded with a 14.3%  increase in open rate with the email line, “We still haven’t received your {{product_name}}”.  Most importantly, that email triggered an 8.6% increase in customer send-in rate.

What we learned

We were encouraged by uSell’s thoughtful approach in looking beyond open and click rates. Best practices in email marketing focuses on the basic testing of frontend touchpoints like open and click rates.  However, in service-oriented businesses, it is more important to think about action and note that true engagement might need to be measured elsewhere.

We know that transactional email is important because it sees higher open and click rates because typically these are the emails people want to see (payment receipts, password resets, signups etc). Because transactional email is critical to various engagement points (in uSell’s case, critical to a customer sending in a device), it is very important to measure the performance of individual emails.

What’s especially encouraging about uSell’s case is their ability to use transactional email testing to increase engagement on one side of their marketplace, and using Sendwithus to test for an offline conversion point.

If you think you could benefit from transactional A/B testing, sign up and try it free.

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2 responses to “Case Study: A/B Test Transactional Email For an 8.6% Conversion Lift”

  1. […] #46 Sendwithus, a transactional email provider, improved uSell’s transactional email performance by 8.6% The overview: uSell, a company helping their customer to sell their used gadgets, could improve their conversion rate by 8.6% by actually measuring the end result of the emails sent, instead of just the email open and click through rates. Key findings: Over the long term, measuring engagement resulting from the email campaigns is more meaningful than measuring only open and click-through rates. A higher open rate or click-through rate can mean a lower overall engagement rate. So always measure the final outcome. The original: Case Study: A/B Test Transactional Email For an 8.6% Conversion Lift […]

  2. […] A/B Test Transactional Email For an 8.6% Conversion Lift – Online marketplace uSell achieved 24.5% increase in open rate and 8.6% increase in revenue-generating offline conversions through sendwithus transactional email A/B testing. […]