Why does Litmus report more opens than I expected?
Email Analytics works in part through the use of a 1x1 tracking pixel (similar to how your ESP probably provides open rate metrics). Every time this pixel is re-loaded, we will detect an open of your campaign.
If you included the tracking code in your email, and continued making modifications to the email (either by previewing it in a template in your ESP, or previewing in a local browser during design and development), the code will collect opens during this time.
Email Analytics reports opens as total opens (as opposed to unique opens). This means that multiple opens by the same person will be displayed, and multiple opens may be collected if that person re-loaded images in the preview pane and later in a full browser view.
We may report a higher number of total opens than your ESP or mailing provider. This is common, and is due to differences in how Litmus tracks opens compared to other providers. Sometimes email clients will make several calls to load the images in an email after the initial open, either because of a bug on their end, or in order to ensure that the graphics load quickly. Some providers run queries behind their reporting that will analyze and "throw away" a subset of these multiple hits (i.e. if more than 4 hits are recorded in less than 1 second, it may only be counted as one hit). Litmus doesn't throw any hits away.
Other things that can contribute to a higher open count in Litmus are: testing and preview data while the email is still in development, the number of "view as a web page" views, prints, and forwards. If an email that contains a tracking code has been shared (posted to a website, shared on Twitter, in a blog, etc.), Litmus will also continue to collect "opens" when images are loaded in these situations.
There is also the possibility that the tracking code was used in more than one email, or is being used in a template that has been the basis for many emails sent out.