How can I get out of the Google spam list if a domain name delegated to Yandex got into it?

Question

Yandex

Good afternoon.
The problem is the following: there is a domain name delegated to Yandex. The site itself is hosted on nic.ru, mail, respectively, works on the basis of Yandex. Recently, apparently due to a hack through a Wordpress vulnerability and subsequent mailings, we ended up on the Google spam list.
We receive the following messages:

This is the mail system at host yandex.ru.
I'm sorry to have to inform you that your message could not
be delivered to one or more recipients. It's attached below.
Please do not reply to this message.
: host ASPMX.L.GOOGLE.com[2a00:1450:4010:c04::1b] said:
550-5.7.1 [2a02:6b8:0:801::1 12] Our system has detected that this
message 550- 5.7.1 is likely unsolicited mail. To reduce the amount of spam
sent to 550-5.7.1 Gmail, this message has been blocked. Please visit
550-5.7.1 support.google.com/mail/bin/answer.py?hl=en&answer...
for 550 5.7.1 more information. s18si15389839lbv.17 - gsmtp (in reply to
end of DATA command)

We have the DKIM tag enabled. In principle, all letters are designed according to guidelines.
At the same time, part of the letters is sent if the subject of the letter is changed each time. With a probability of 100 percent, letters with the words "RE:" in the subject line do not pass.
Unfortunately, this greatly interferes with work. I really ask for help, because changing the domain is not an option for us at all.

Answer 1

You can't apply to Google to be excluded from the spam list. When contacting Google technical support, they are
usually advised to perform the following steps , and if it doesn’t help, they are sent here
pop up.