My emails end up in spam - what should I do?

Question

Email

Letters from my corporate mail info[@]adlab.ee end up in spam for many people.
I connected mail to Yandex servers. In support they say that they cannot help - it is necessary to solve the problem on the side of the mail servers of the recipients of the letters.
How can I find out the mail server of the recipients of my letters, if they all have mail in their domain zone like [email protected]_firmy.ru
In the logs of the sent letter, you can find out?
*By the way, I don't do mailing lists, but I send individual letters to clients. The problem is even with those with whom I had previously corresponded.
Please advise something.

Answer 1

https://mxtoolbox.com/SuperTool.aspx?action=mx%3aa...
Look at DMARC for starters, then you can reproduce standard gestures like DCIM checks, server responses, public spam databases, etc.
You will see where the jamb is.

Answer 2

Check if authentication is configured in emails: https://www.unisender.com/ru/blog/haki/kak-nastroi...
After that, you can go through this checklist: https://www.unisender.com/ru/ blog/advice/your-pis...