Visit your domain registrars website. We will use Cloudflare as an example but the workflow is similar to most registrars.
Go to your Domains DNS settings
Now you should see something similar to this:
Delete all existing MX records
Add both of the following MX records:
Type: MX Host/Value/Name: @ or your domain in case @ does not work Value/Target: mail.vgl.marketing Priority: 10
Type: MX Host/Value/Name: @ or your domain in case @ does not work Value/Target: mail-relay.vgl.marketing Priority: 20
Add the following two TXT record
Type: TXT Host/Value/Name: @ or your domain in case @ does not work Value/Target: v=spf1 include:mxlogin.com -all
Type: TXT Host/Value/Name: x._domainkey Value/Target: The DKIM key you copied earlier. If you hit failure later, try doing this again but NOT selecting the quotations at the beginning and end. Some DNS providers add their own quotations.