That is a tough one.. yes they can be used, but, if your ex denies the email was sent by him then it can be costly to prove overwise.
For a recent example, you just have to look at the Microsoft case. Microsoft managed to get a court order to seize Netscape's mail backups and used their emails against them.
In your case, it can be depend where he sent them from and where they were sent to. Were any work email used in the exchange ?..
This is a close subject for me as in 3 weeks we will be in court and using emails to show something. The emails were sent from his work address. If the person denies the exisitance of the emails then I will look to get a court order to seize the network and email logs. It is a major company and I would probably not get far, but I know the threat of this order would be enough to scare the person as they would be fired !
As regards to general email from a normal ISP account, then the header information is enough to enable a trace. They can trace that it was sent on a specific date, that the person who sent it logged on at such a time and dialed in from a certain number. These are all things that pin point the origin of the person... but this gets expensive to prove.
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SMILE - Start Making It Livable for Everyone
Divorce is a process over which children have no control. Children should not be its victims.
When parents are under stress, it is harder to be in touch with their children's pain and anguish.
It takes time, effort, and planning on the part of the parents to be able to provide for the children's needs.
In the crisis of divorce, parents may put their children on hold while they attend to adult problems first.
Sometimes separating/divorced parents find that their roles and expectations are undefined and cloudy.
If handled properly, divorce need not be devastating for children.