What are the options to send emails not to spam on WordPress?

Question

Domain Name System

Good afternoon. Such situation. In the DNS of the domain name, the MX record of the Protonmail mailer. The record cannot be changed, mail is needed on Protonmail. To connect via smtp, you need to dance with a tambourine on the server, according to this article. There is no access to the server, only hosting, but sending them an article asking them to "do this" seems like a bad option. Php mail also seems to be out of the question because there is no command line access. Site on WordPress. Mail is currently sent via the WP Mail SMTP plugin and @gmail.com mail. Mail.ru and gmail.com accept them normally, yandex.ru sends them to spam.
The question is, what options do not send letters to spam in this case?

Answer 1

MX has nothing to do with it at all. Is there an SPF? DKIM? DMARC?
SPF needs to be adjusted if not.

Mail is now sent via the WP Mail SMTP plugin and email @gmail.com

This is the most normal option, you can’t set up your smtp better than Google.

The question is, what options do not send letters to spam in this case?

If everything is OK with SPF / DMARC, then the option is not to send spam.
Test your emails at https://www.mail-tester.com/

Answer 2

Good afternoon!
Read this article
https://7fk.ru/nastroyka-smtp/
And yet, do you know that Protonmail cannot work with mail ru, for example?