is it legal to read others e mail??

Discounting the fact that it's very uncool to read other people's email, even in a case like this, I'm pretty sure that's inadmissible. You should probably ask a lawyer instead of asking here.

The answer to that question is going to depend on the State in which the case is heard. I am personally unaware of any cases which have addressed this issue. This question is a perfect example of where technology has advanced faster than the ability of the law to keep pace.

My personal hunch is that this situation is no different from a situation where an individual left paper work behind. While it is illegal to open "snail" mail addressed to another, that rule is a specific federal statute dealing with the U.S. Postal Service. Obviously, e-mail is not part of the U.S. Postal service and is not subject to that statute. The one complicating factor is that access to e-mail is by telecommunications. If courts view this situation as being a version of telephone communications (between the ex and those mailing him), interception of such communications by a third party would be illegal.

Some of the previous answers raise the issue of hearsay. To the extent that a hearsay objection might have merit, it would be possible to subpoena internet service provider and the other party to get around that objection. In providing my answer, I am assuming an argument about whether there would be a rule against using the information from the e-mail to obtain admissible evidence.

I don't think so. It's probably considered hearsay and if she has his passwords without his knowledge, that's probably illegal. I worked in a Family Law office for three years and saw something similar backfire. I wouldn't do it.

It's not right and her ex husband should not have left his passwords.

Nope. He could take legal action against her if he finds out she is reading them.

It's invasion of privacy even if they are married.

Fourth Amendment: no illegal search and seizure.

So no, she cannot.

as long as she didn't hack into his business, it's all free game.