DKIM signs your outgoing emails with the use of an encrypted key which is used during verification by MTAs. It is the best method of protecting your emails from hackers and abuse. For Plesk to begin signing your emails each time you send a mail, you need to enable DKIM. Refer below-mentioned steps for How to generate DKIM record for my domain in Plesk server?

Note: DKIM is enabled for Plesk by default.

But if you want to enable it for a custom domain, follow the steps below:

• In case you use Plesk as your DNS provider, go to Websites & Domains > your domain > the “Mail” tab > Mail Settings.
• Locate the “Use DKIM spam protection system to sign outgoing email messages” checkbox and enable it.
• In case you use an external DNS server, you need to manually add the DKIM records for Plesk to your DNS by generating them on Plesk.
• To do so, click on “How to configure external DNS”
• Copy the 2 DNS records that are there:

• Now you can log in to your DNS and publish the record in the DNS records section to enable DKIM and save changes
• It will take 24-48 hours for your DNS to process these changes.