[lproven]

This is true. OTOH, I do think the problem is solvable.

I came up with a routine to parse and translate about 2-3GB of saved emails into MBox format once.

The official delimiter is unbelievable, IMHO.

« the exact character sequence of "From", followed by a single Space character (0x20), an email address of some kind, another Space character, a timestamp sequence of some kind, and an end-of-line marker. »

https://datatracker.ietf.org/doc/html/rfc4155

https://en.wikipedia.org/wiki/Mbox

That's it. An email is a section of text beginning with

From $something

That's the spec.

[immibis]

Certain software used to add a > before any line starting with From in an email body because of this.