Yes, on an organisation/company Internet/Intranet system emails are retained in line with the freedom of information, which has been highlighted recently in a few cases where people have got into trouble over what they have said in an email, even an internal one. That happens now, not in the future.
ISP's also retain that information for other reasons, as far as your spouse getting hold of that information, no chance, unless he/she obtains a court order and you've got to have a very good reason indeed to obtain one.
Incidentally, phone calls are not recorded, unless you are warned, like calling a call centre when they tell you calls are being recorded.
OCTAL is right about emails being retrieved easily by employers. Most [not all] route through a server that logs each email. These records are then backed-up so, in theory, they can gain access to any/every email sent or received. The only question is how long they back-up for [my employer has a 12 month tape system that i know of, but may have others - see next paragraph]. Obviously, ISPs have a longer timescale and, I am told, this is enforced by law rather than being left to them to decide - but you need a VERY good reason to access these such as National Security. They also log all internet activity for the same reason.
With reference to phone calls being recorded, I work for a multi-national company with special links to Defence in most large countries. ALL calls [ingoing and outgoing] are recorded - I've seen the huge disks they use - and it is part of our contract that we accept this. There is no warning to incoming callers that this is being done [although most know about it anyhow] as we have special dispensation in view of our'special' status .....