问题
Before you dismiss this question because it "makes no sense" and "it's impossible" please hear me out:
The issue:
We implement a tracking pixel (i downloadable GIF file with a unique URL) in each email that we send using our system, this helps us track opening of email messages. The problem with this is, that when we cc a few recipients the tracking pixel is downloaded and we can not detect who has opened this email, since all emails are CC'ed the content must be the same.
Possible solution:
If the SMTP server were to control injecting the tracking pixel, the SMTP can change the message body from recipient to recipient by posting each recipient with a different URL, pretending that all recipients received the same message.
However, using a public SMTP server (e.g. Google's SMTP) this does not seem possible, yet there are companies (AirMail for example) that still are able to do this, sending different content (different tracking URL per recipient in a cc message). When I check the email headers they seems to have been sent from googles SMTP server (clients account uses a gmail.com account). How is this possible?
回答1:
They are creating a unique message for each individual. Nothing really magical. Usually some type of mail merge.
来源：https://stackoverflow.com/questions/39480102/sending-a-single-email-message-with-different-content-for-each-recipient-using