just brew it! wrote:
As already explained, a plain text file is very unlikely to be acceptable as evidence, no matter how it was produced. It is too easy to fake.
Have you spoken to a lawyer yet?
Speaking to a lawyer is absolutely the starting point.
That said, I'm not convinced that plain text is going to have no value as evidence... It's essentially just like a witness statement and we allow witnesses to give evidence in court. If it comes down to "I say you said this, you say you said that" then I presume the network operators would get called in rather than relying on anything on anyone's phone. IANAL but authenticating evidence is only important if it's disputed and you've got to be pretty stupid to dispute something you know you sent in a text message because the network operator will be able to authenticate it so you're perjuring yourself for no gain.
All that said I'd just go to messages.android.com on your computer and copy and paste the conversation into a text editor. This assumes you use the google "messages" sms app)
Alternatively I'd consider using airdroid to access your sms in your computer's browser and again just copy and pasting. That should work with any standard sms app but won't work with things like signal or facebook messenger.