Internet service provider (ISP) is your local link to your computer in the world of computer network know as Internet. Every page you request from Internet and every communication you have done on Internet is travel through your ISP servers first. Even anyone can not use World Wide Web (www) without ISP as we all know.
But it can’t get every bit of information because it costs a lot for ISP to store all data. It is also not possible due to out of law of public privacy.
However, ISPSs can do track the online behaviour of suspects targeted by Homeland and Investigation Agencies for terrorism investigations or other suspicious activities.
In European Countries, ISPs are now required by regulation to save e-mails logs for up to two years.The e-mail logs do not contain e-mail content but store the information of who send the messages and to whom and when messages are send. Logs can be investigated by investigation agencies if required.