Not accurate
I sent myself a few test emails. The IP address and the device types registered in my test are the same as the recipients I sent emails to that I was looking to track. Somehow in the background it picks up a ping from your device then registered it as an open.
Response from developer
Hello, thanks for flagging this! What you're seeing is your own Mail app loading the tracking pixel as the email sends, which can show up as an "open" from your own device and IP. We've already pushed a fix on our end to filter these out, so your tracking should read more accurately going forward. If anything still looks off, email us and we'll sort it out for you. Thanks for giving us a shot to make it right.
