Sendmail Ubuntu. Why always in spam?

Question

PHP

Yesterday I created a server on digitalocean.
Installed Sendmail. Sends letters, but always in spam. I also indicate the author, and the text is normal. Already googling everything, no strength. Tell

Answer 1

A valid ptr entry is required. It is configured in the DO control panel.

Answer 2

https://yandex.ru/support/pdd/set-mail/spf.xml
In general, connect Yandex traffic rules or Mail.ru for Business.

Answer 3

You need to do:
Optionally, you can also add a dmark entry to dns, but the two points above are mandatory.