WordPress Emails - Mailed By

Hi,

I have two WordPress sites on a droplet.

• domain1.com (subdomain.domain1.com as hostname)
• domain2.com

When a user registered an account on domain2.com, an activation email sent to the user. But the “mailed by:” in the header shows that it’s mailed by domain1.com.

The signed by is correct, which is signed by domain2.com.

I guess that’s the reason why it gets into spam folder? Because it’s mailed by other domain.

How do I set it to have domain2.com (and any other domains on the droplet) to be mailed by its own domain? e.g. domain2.com, mailed by domain2.com. e.g. domain3.com, mailed by domain3.com.

I have Postfix and OpenDKIM on the droplet.

Thank you.