Has anyone decoded this message from Deus Ex: Mankind Divided?

Very hard to find out. We don't even know the set of character used to encrypt that message (if there's a message behind it). It's not ASCII standard because of @ and #, and it's not a standard Base64 encoding for the same reason (I already tried every source of characters, btw).

So it must be a sub-set of Unicode, my guess is a ROT-47 alphabet. This, at least, contains every character used in the email:

!"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz{|}~

or maybe a custom set of Base64 containing those two symbols (as per @NickKennedy's comment):

ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789@#

Now the hardest part: discover the encryption method used.

I had no luck with Caesar's cipher, I tried all combinations using a quick Java program, even with different alphabets.

Other methods like Polybius, Delastelle, Atbash, Rail fence, Playfair and even Enigma machine seems unlikely because we have both uppercase/lowercase letters, numbers and those 2 symbols.

So my guess will be on Vigenere cipher, since it was used for another encrypted email:

But again, we may have the same problem: "where's the goddam key?". That enigma already had a big hint to solve the puzzle, since...

the actual key to decrypt it was a sentence in the email.

I don't own the game so I can't investigate, but the key may be, again, under our noses...

Anyway, nobody has decrypted this yet in years, so maybe there's nothing to discover.