Why does Yandex mail not understand html tags in a letter?

Question

HTML

Greetings!
I send a letter from the site, Gmail understands html tags and everything is OK, but Yandex and Mail.ru simply displays the html code. Why ?
An example of how a Yandex letter is displayed:

Answer 1

According to the standard , an HTML letter must contain a Plain part that matches the text.
That is, if you look at the source code of the letter, then the main headings should indicate

Content-Type: multipart/alternative;boundary=<строка-разделитель>

Then there should be two parts of the letter:
- pure text with Content-type: text/plain;charset=utf-8
- HTML part withContent-type: text/html;charset=utf-8

Answer 2

Yes, when sending a letter on Yandex, only the second and only part is formed:
Content-Type: text/html; charset=utf-8
Therefore, when a letter gets into the mailing list, for example, a system configured to receive only the text part does not see the html and simply cuts it off, as a result, users do not see the message, which is very inconvenient. I wrote to support so that they fix the system in accordance with the standard, or they will have to return to Gmail, which, by the way, works correctly in this regard: clear text is displayed in mailing lists, when users receive a letter, they see beautiful formatted html text.