Correctly taking into account the open rate can be difficult due to technical limitations.
The tracking pixel allows you to track openings - a unique picture in each letter, the opening is fixed when it is loaded.
But the user may have images disabled, in which case the opening will not be counted. Conversely, if the user has the image preview function enabled, then the opening will be counted, although, in reality, the person may not read the letter.
In our case, all manipulations with warmup emails are done using IMAP requests (reading, moving from folders, replies, and notes). These requests do not open or download the pixel in the email since the manipulation is done through requests, not via a browser or email client.