Regarding your number 2... Frequently get tampered with in transit? Really? I have, literally, never seen this....
You're lucky there. I see such tampering several times per day, and fixing the problem often takes a lot of time (and soto-voce swearing
The reason is that I deal with a lot of data that's "plain text", but is computer data of some sort, not a natural language like English (which is sorts stretching the meaning of "natural", but you know what I mean). Or it's in a human language, but not English, and the character encoding uses some 2-byte or longer characters.
The simplest example is computer source code. The tampering is often caused by the "punch-card mentality" coded into a lot of email software, which often doesn't allow lines longer than 80 (or 72) characters, and inserts line feeds to make everything fit. Many programming languages consider line feeds to mean something different than a space, usually "end of statement". Inserting a line feed in the middle of a statement thus changes the meaning, and very often introduces a syntax error.
Even nastier is the munging a lot of other plain-text data representation that mixes letters and numbers. Inserting spaces or a line feed in the middle of a token like "G2EF" usually destroys the meaning in a way that can't be corrected automatically at the receiving end. Usually the way to handle such tampering is to reply to the sender, saying "Can you send me that in quoted-printable or base-64 form?" And you try to teach everyone in the group that such data should always be encoded in a form that's immune to the idiocies of "smart" email handlers.
Text in UTF-8 form, especially Chinese and Japanese text, is especially prone to this sort of tampering, which often leaves the text garbled beyond recovery.
Anyway, there are lots of excuses for such tampering with email in ways that destroy the content. It's not always for nefarious reasons; it's just because the programmers only tested their email-handling code on English-language text. And because they're idiots who think that lines of text should never be longer than 80 (or 72) characters.