Hi,
I just wondered if anyone had used anything to track emails being sent.
For example when and and if they were opened, for how long etc?
A client has asked if he can do this with emails he sends out and there are so many out there I'm not sure which one to go for and just wondered if anyone else had used any.
I was looking into Read Notify but there is a 2000 email limit on that and it will probably be about 5000-6000.
Thanks
Suzy 
I can't remember if Campaign Monitor tells you for how long an email was viewed, but we've been pleased with the sort of data it returns: number of messages viewed, number of viewed messages that resulted in some other action (e.g. going to any one of a set of urls, unsubscribed, etc.)
Thanks I'll take a look 
Seconded for Campaign Monitor. We use it for a few of our clients and the reports are top notch. Easy to template too.