Follow this tutorial to use External DNS Service with Plesk for example Cloudflare

1. Log in to your Plesk account.

2. Click on Websites & Domains from the Sidebar Menu

3. Click on Hosting & DNS then on DNS Settings

4. You will see a page like this

5. From here copy and paste the necessary DNS information to your External DNS Service

For website, create the following records on your External DNS Service:

• A record
  • name: yourdomain.com
  • content: IP address you see on your panel
• CNAME record
  • name: www.yourdomain.com
  • content: yourdomain.com

For webmail, create the following records on your External DNS Service:

• A record
  • name: webmail.yourdomain.com
  • content: IP Address you see on your panel
• A record
  • name: mail.yourdomain.com
  • content: IP Address you see on your panel
• MX record
  • name: yourdomain.com
  • content: mail.yourdomain.com
  • priority: 10
• TXT record
  • name: yourdomain.com 
  • content: v=spf1 +a +mx +a... Copy the full content from your panel
• TXT record
  • name: default._domainkey.yourdomain.com
  • content: v=DKIM1; p=... Copy the full content from your panel

Once you are done you will be able to access your website and your webmail.