Why is the SSL certificate for mail yellow (untrusted)?

Question

Digital certificates

I do not quite understand why the certificate is yellow. Can you please tell me where to check the mail settings?

The certificate is paid.
Because of this, as I understand it, letters to mail.ru, inbox.lv and other services do not come. On yandex.ru, one-time mails (through the service) receive letters there.

Answer 1

Changed the SMTP HELO/EHLO mail server settings from a**.hoster.zone to bigpay.eu (website domain) and it all worked. Letters come to all mailboxes + the signature is confirmed.

Answer 2

No, not because of this. A valid certificate is not particularly needed, a self-signed one is enough.
And where is your "yellow"?