Emails from google appengine not reaching mail.ru?

Question

Google Workspace

I send emails using the google.appengine.api.mail service to the mail.ru address
Application domain *.appspot.com Sender
address "Name <[email protected]>"
Message body contains either text/html or text/html + text/ plain.
Something like this content:

Превед %USERNAME%! <br/>
Вы зарегистрировались на сайте или сменили email.<br/>
Для подтверждения сего перейдите по ссылке: <a href="http://блаблабла?code=xxx">блаблабла?code=xxx</a><br/>

None of the test emails got through, were not forwarded, and did not end up in spam.
When sending on the gae side, no exceptions fell out.
How to diagnose such problems in general?
Is there a solution?

Answer 1

I had a situation when my letters did not reach mail.ru (I got an auto-reply that it was spam). The body of the letter was formed in a WYSIWYG editor.
Asked a question in mail.ru. It turned out that AdBlock for safari (like any WebKit, I guess) inserted its ad-blocking codes inside the html emails. And since there were words like Ad and so on, mail.ru considered it to be spam.
I did not see any of this myself, because these words were embedded in the styles and were not visually shown. And it never occurred to me to look at the code of the received letter.

Answer 2

In tech.pod. mail.ru did not write?