Mail sent from a WordPress site fails quietly. Order confirmations, password resets and form notifications are accepted by the sending server, and then filed as spam by the receiving one. The usual reason is that the domain never published the three DNS records that prove the mail is really yours.
This plugin reads those records and tells you what they say.
What it checks
Two of these are worth stating on their own, because they are the failures people miss. A second SPF record does not add a sender, it switches SPF off. A second DMARC record does the same to DMARC. Both look harmless in a DNS panel and both are found by this plugin.
Every finding comes with an explanation in ordinary words and the exact change to make.
No external service
Every lookup is a plain DNS query made by your own server through PHP. Nothing about your site, your domain or your records is sent to any third party, and the plugin has no account, no key and no upsell. Results are cached for one hour and can be refreshed from the page.
Where to find it
Tools, then Email Auth Check. You need the manage_options capability.