

Email filters can strip them out, and the recipient’s email program might not automatically load images when an email is opened. They are much more reliable than read receipts but are not 100% reliable. Email web bugs require special software and are not trivial to implement (for example, when sending from Outlook or Mac Mail).

If they are, it means the message was opened.
How do you know if an email was received? There could be significant delays or consequences if the message was not delivered. You just sent an important business communication via email and assume all is well, but what if that email was not received?
