Horizon Hosting

Support guide

Why is my email being blocked?

A common reason for rejected mail—and the steps your email provider can take to fix it.

The most common cause: reverse DNS

If you’re having trouble sending to an email address hosted by Horizon Hosting, the sending mail server may have missing or incorrect reverse DNS.

Reverse DNS links a server’s IP address back to its hostname. It helps receiving mail systems verify where a message came from and is a widely used protection against spam and malicious email.

Why the message is rejected

A server without valid reverse DNS is harder to verify. To protect hosted mailboxes, messages from an unverifiable server may be refused before delivery.

How the check works

1. Server connectsThe sending mail server identifies itself and connects from an IP address.
2. Address is checkedThe receiving server looks for a PTR record that maps the IP address to a hostname.
3. Identity is verifiedThe hostname and address should resolve consistently. If they don’t, the message may be rejected.

How to fix it

  1. 1
    Contact the sending email provider

    Ask whoever manages the sending server to check its hostname, forward DNS and PTR record.

  2. 2
    Use a static IP address

    If the mail server uses a dynamic address, ask the internet provider about a static IP with correct reverse DNS.

  3. 3
    Use an authenticated relay

    Alternatively, send through your provider’s correctly configured SMTP relay, sometimes called a smart host.