I agree, mail deliverability is really hard. In my case, the mailserver is only used to use a custom email address and forward the email, so deliverability was

I agree, mail deliverability is really hard. In my case, the mailserver is only used to use a custom email address and forward the email, so deliverability was not an issue but other people using my domain name to send phishing emails. By making the fixes mentioned in the article the phishing attacks were stopped.