Can emails between my ex-wife and myself be used in court to rebut her testimony under oath?
Are they admissable as evidence?
Can emails from a third party be used in court proceedings if third party is not present in court room?
If you can authenticate the emails between you and your wife, then yes, they can be used to both rebut her testimony (this is easier) and they can be admissible as evidence.
Emails from a third party will not be admissible if they are not present in the courtroom unless there is some way you can properly authenticate them. Even then, the content of the email may be inadmissible hearsay.
I have a question about your answer.
How do you authenticate the e-mails?
It’s a process dictated by the rules of evidence. You need to provide a proper foundation, meaning explain to the court how you obtained this evidence, that it wasn’t altered in any way, that it came to your email from the other party’s email address, that you are familiar with the other party’s email address, and things of that nature.
Normally, authentication is not difficult until the other party begins objecting to the validity of the evidence.