Mail, why unreliable sender?

Question

SPF

Good afternoon,
I use Yandex traffic rules for the domain, but I send mail via sendmail, because There are over 500 emails per day.
Set up sendmail and opendkim

dnl#
define(`confCACERT_PATH', `/etc/letsencrypt/live/doamin.ru')dnl
define(`confCACERT', `/etc/letsencrypt/live/doamin.ru/chain.pem')dnl
define(`confSERVER_CERT', `/etc/letsencrypt/live/doamin.ru/cert.pem')dnl
define(`confSERVER_KEY', `/etc/letsencrypt/live/doamin.ru/privkey.pem')dnl
dnl#

INPUT_MAIL_FILTER(`opendkim', `S=inet:[email protected]')dnl

opendkim.conf

Selector        1111111111.domain
KeyFile /etc/mail/dkim.key

Added records to DNS

1111111111.domain._domainkey.domain.ru TXT v=DKIM1;k=rsa;t=s;p=MIG...AB
mail._domainkey.doamin.ru TXT v=DKIM1; k=rsa; t=s; p=MIG...AB  # - для Яндекса
domain.ru TXT v=spf1 include:_spf.yandex.net include:domain.ru ~all

The ptr entry is set.
Both Yandex and Google write about possible spam.
What could be the problem?

Answer 1

Check on these testers:
1. https://www.mail-tester.com/
2. https://glockapps.com/