I'll check your domain name and make sure that all the systems that should be allowed to send emails can do so properly, and that nobody else can send emails claiming to be from your domain, using the relevant SPF and DKIM records. This will help prevent the type of filtering that happens before the content is even looked at by anti-spam systems.
I've spent close to a decade now working on the more technical side of email, and it irritates me that so few email systems are set up even half properly. <rant>I also don't like the quantity of spam emails that could easily be filtered out if everyone just caught up with a technology that has existed since the start of the millennium.</rant>
Email Deliverability Expert & Fixer of Internets
Very briefly, SPF and DKIM help with email authentication, in other words they make sure emails claiming to be from email@example.com actually came from someone authorised to use the domain example.com.
Why does this matter? Simple, if you don't have some sort of authentication system in place anyone can send from your email address. The system that gets these emails claiming to be from you won't have any reason to believe they aren't. This is called email address spoofing.
Let's say your email address has been spoofed (it probably has). When you try to send out your legitimate emails spam filters will be skeptical. They might have gone as far as outright blacklisting your domain because of all the fake Viagra you were trying to sell last week by email... how were they to know it wasn't you who sent all the spam?
Emails from these systems are actually from my domain, anything else is fake and should be ignored.A Good SPF Record
That's how many domains I look at that are not set up correctly.
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