Note that 0x3D is the "=" character in ASCII, so "=3D" in QP is "=" in ASCII. :)

This email has probably been through a few conversions to QP and back again between different email clients. Perhaps some buggy client got confused between an ASCII "=" and a QP escape sequence or something like that.

Basically: it's a form of escaping, and like other forms of escaping the escape character itself has to be represented as an escape sequence.

So in other languages where \ is the escape character, you have to put \\ to represent an actual slash rather than the start of an escape sequence. Here = is the escape character followed by the hex of the character, so to represent a literal = it needs its own hex value 3D after it.