The only really foolproof way is to convert the text to a bitmap and then OCR it, to ensure you aren't trapped by lookalike glpyhs or varying spaces. (OCR will generally make all spaces single, since spacing varies so widely in practice due to things like justification. It also usually makes all quotes straight since the per-font variation makes it too hard to distinguish open/close quotes.)

You can do this easily enough on MacOS simply by taking a screenshot, pasting it into Preview, selecting the text with its automatic OCR, and copying.

Of course you still need to worry about whether line lengths are varied per-recipient, or even the wording of the e-mail itself. But the above will at least take care of glyphs.

There's a rather old service to clean such copy. It's a called a printer and while it will remove spacing and other invisible characters, the process of printing onto paper hardly ever works. Despite hardware for doing so have been on market for decades.

It's often a good idea to check for weird characters in a text file. Something like this:

cat file.txt | perl -C63 -pe '$_ = join("\n", split(//, $_));' | sort | uniq -c

I've found lots of errors that way: BOMs in the middle of a file, different kinds of dash, quotation marks or brackets that don't match, ...

Paraphrasing would help identifying person by writing style, IIRC by leaking specialist. It could also erase hidden signals in the message.

Just use a for loop in Python over all characters and ignore each char that is not in the ASCII range of letters, numbers and punctuation. Or retype by hand if you don't know Python.

if the steganography signature is unique to the user receiving the content, then you might have to diff it with someone else's to see it (otherwise, you cannot really guess where the changes are which steganographically stores your identity).

If it is the same content for all users receiving the text, then you can just retype the text (not copy/paste) into a different file. Of course, authenticity comes to question if you whistleblow by doing this.

Translate it back & forth. It'll as a bonus also clear out any specific words used to trap you.

Retyping it by hand is far safer.

It could be only hidden characters, but it could also be (and it most likely actually is also) a few commas instead of full stops, words like "many" replaced by "a lot of" or any other kind of substitution really.

Copy paste the text into and console text editor. Should easily see the "hidden" characters, then.

Do a search-and-replace to change all double spaces to single.

RegExp