Encoding of attachment names when sending mail

Tell me, why does Outlook break the original name into segments when encoding the file name in an attachment?

Content-Disposition: attachment; filename= "=?utf-8?B?0KHQstC+0LTQvdGL0Lkg0L7RgtGH0LXRgiDQt9CwINCh0LXQvdGC0Y/QsdGA?= =?utf-8?B?0YwueGxzeA==?="; size=379865;

Are these any features of this encoding?

For example, when koi8-r is used, I don't notice this...

In the beginning, I thought it was outlook doing some sort of alignments and all that, but if you remove this, then there are problems with file naming.

This is a continuation of this topics

Author: iluxa1810, 2020-09-28