I see no specific issue with sanebox.com, however it appears that they are only offering a service you can do on your own. Honestly, do you really get that much SPAM? Source: over 1 year ago

Also, send email messages from your domain to https://unspam.email/ and https://www.mail-tester.com/ for analysis of deliverability issues. Source: over 1 year ago

Use deliverability tools like https://unspam.email/ for more analysis. At least, you'll be able to see via the headers whether everything is configured correctly. Is the WP site hosted on a VPS or do you have the ability to look at the config files / logs on the host ? Source: almost 2 years ago

Getting a bunch of warnings from https://unspam.email/ that I cannot seem to figure out how to clear up, they are the following list. I will gladly pay $15 for someone to help me get these issues resolved (without creating more issues), I have full control over the DNS. Source: over 2 years ago

Unspam is currently available for 30% off with the code “BLACK” until November 30. - Source: dev.to / over 2 years ago

Try services like https://unspam.email/, and it will scan your reputation and deliverability. With the output feedback, you can work and decide what works badly. Source: about 3 years ago