DKIM in the WordPress Newsletter plugin.
DKIM stands for DomainKeys Identified Mail and is used by remote email servers that receive emails sent from the WordPress Newsletter plugin to verify the identity of the origin or sender of the newsletter/email.
Enable DKIM for Outgoing Emails
There are various ways of turning on DKIM for emails depending on your setup:
1. Using the Newsletters Plugin
We recommend that you use the DKIM inside the WordPress Newsletter plugin itself when you’re using any type of SMTP server which may not turn on DKIM for you. That way the plugin will generate everything for you and do the DKIM.
You’ll find a DKIM wizard in the plugin under Newsletters > Configuration > General > General Mail Settings which will walk you through the steps of setting up DKIM accordingly. See the DKIM wizard documentation for more information.
2. Inside Hosting Control Panel
If you are sending emails using your local mail exchange, you can turn on DKIM inside your hosting control panel. If you are using cPanel, see their Email Authentication documentation which tells you more about enabling DKIM. It’s as easy as just turning it on.
3. Email Provider/Relay Service
For other email relay services such as Amazon SES, SendGrid, MailGun, MailJet, Sparkpost, etc. they have DKIM settings built in which can be turned on. See the relevant documentation or instructions on how to turn on DKIM for your specific email service provider.