[Mailman-Developers] Mailman3 replaces [ with =?utf-8?q?=5B, why?

Hi all,

I've seen these Subject: lines being changed using utf-8 quoted-printable encoding for every non-alnum character. The message has: X-Mailman-Version: 3.3.9rc4.

Of course, doing so breaks DKIM signatures, and I'm trying to understand in what cases it is advisable to revert the encoding in order to verify the signature. Does Mailman 3 always and unconditionally behave like that or what does it depend on?

TIA for any hint Best Ale

P.S. I'm curious to see how this Subject: is going to be encoded by Thunderbird. Original-Subject: Mailman3 replaces [ with =?utf-8?q?=5B, why?