As far as I know, the only way to see what a message says is to load up the game as the receiving empire. I write all my Messages in wordpad and save it after copy&pasting into the game. I also copy&paste all Messages received into the text file and mark each message with "sent" or "received" and the game turn. One file per other empire and one directory per game makes looking things up very easy.
Hmmm...I thought I would need pen and paper , the cut and past may be cool have to give it a try, the other you would need players password to gain access to the message there
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Kill em all let God sort em out
I too keep all of my Messages in word pad or note pad format. You can also use the in game NOTE: feature and save any in coming or out going message simply by copying and pasting to it.
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Creator of the Star Trek Mod - AST Mod - 78 Ship Sets - Conquest Mod - Atrocities Star Wars Mod - Galaxy Reborn Mod - and Subterfuge Mod.
I use PIM software (InfoAngel) to store diplomatic Messages. It's quite comfortable, since you can create a folder (game name), subfolders (empires) and notes in each subfolder (Messages itself).