I am currently using www.readnotify.com which has a lot of good
features but 25% of the time the reports show "not opened" after
opening (I know because I receive replies).  I have tried changing
settings, etc. The other services I found seemed to have less features
(www.didtheyreadit.com,www.pointofmail.com) or be linked to the same
services under a different name (affiliates). I have Emailtracker Pro
for incoming mail.

Is there a more advanced service or software with higher level of
accuracy? Is there a program that is better at tracking the "real ip"
as opposed to the server ip or a proxy?

A good answer will include names/links to a more advanced emailtracker
than readnotify and if possible links to unbiased reviews (ie not from
sites that sell the software they review) of various tracking
services.