Configuring reverse DNS validation

You can use reverse DNS as an additional form of sender verification. A reverse DNS lookup finds the domain name based on the IP address. Because a reverse DNS lookup enables anyone to view the source of a connection, many bad senders do not have reverse DNS records, or have false reverse DNS records.
  1. To configure reverse DNS validation
  2. In the Control Center, click
    Protocols > SMTP > Settings
    .
  3. On the
    SMTP
    tab, under
    DNS Validation
    , check any of the following options:
    • Reject connections where no reverse DNS record exists for the connecting IP address
    • Reject connections where the reverse DNS record exists for the connecting IP address, but the 'A' or 'AAAA' record of the resulting domain does not match the connecting IP address
    • Reject connections where the domain provided at HELO and EHLO has neither an 'A', nor an 'AAAA', nor an 'MX' record in DNS
    • Reject messages where the domain provided in the MAIL FROM address has neither an 'A', nor an 'AAAA', nor an 'MX' record in DNS
  4. Optionally, you can edit the
    Reject message
    text for any option that you checked.
  5. Click
    Save
    .