If your emails to customers land in spam, the problem usually isn’t what you wrote. It’s that the receiving server can’t confirm the message really came from you.
Three records do that job. They live in your domain’s DNS settings, not on your website, which is why most people have never seen them.
SPF is a list of the servers allowed to send email using your domain name. If a message arrives claiming to be from you but came from a server that isn’t on the list, that’s a flag.
DKIM is a signature. Your mail server signs every outgoing message with a key, and the receiving server checks the signature against a public one published in your DNS. If it matches, the message wasn’t tampered with in transit and it genuinely came from your system.
DMARC ties the two together and tells receiving servers what to do when a message fails — ignore it, quarantine it, or reject it outright. It also lets you receive reports about who is sending mail claiming to be you.
Get all three right and Gmail, Outlook and the rest have a reason to trust you. Get them wrong or leave them missing and you’re asking to be trusted on the strength of nothing.
A few things worth knowing that cost people deliverability without their realising:
Forwarding breaks SPF. If mail is forwarded from one address to another, it arrives at the final destination from the wrong server and fails the check — and the failure counts against whoever forwarded it.
Sending from a Gmail address while your website claims to be your own domain is a mismatch, and a small one that adds up.
And a sudden change in how much mail you send looks suspicious even when it’s legitimate.
If your mail is landing in spam, these are the first things to check, and they’re checkable in minutes.