I have to create email tracking system, but the problem is that when the sender opens an email this is counted as an opening by the recipient.
When I send an email through Polymail (or some other tools for tracking emails), then in the 'sent' folder I have an email without a tracking pixel, but the recipients of this email have the pixel and at the same time everyone have different code inside (I think, to determine which of the recipients opened the email).
How is this possible? The sender and the recipients have different contents of the same email. Can this be implemented using smtp / imap / gmail-api?
For standard IMAP/SMTP setups (specifically: not GMail), the message is submitted twice, once to SMTP to be sent, and again to IMAP to be placed in the Sent mailbox.
There is no requirement that these be the same: in fact, in normal use, the BCC header, for example, is submitted to IMAP, but not SMTP.
GMail, and a few others, while trying to be helpful and save bandwidth, do the copy automatically, but make it impossible to supply different versions. (Unless you want to try to find the duplicates and delete them out of band).