This article explains why Hornetsecurity IP addresses may be listed on UCEPROTECT and what you can do if emails are rejected because of this.

What is UCEPROTECT?

UCEPROTECT is a provider of blocklists. These lists contain IP addresses, network ranges, or ASNs that have been classified as suspicious according to UCEPROTECT’s criteria.

UCEPROTECT publishes several lists with different rating levels. Depending on the list used, not only individual IP addresses but also larger network ranges or entire ASNs can be affected.

Why Can Hornetsecurity IP Addresses Be Listed?

As an email security provider, Hornetsecurity processes large volumes of legitimate emails for many customers. This can include automated emails such as non-delivery reports, delivery confirmations, or out-of-office replies.

Such automated responses are also called backscatter. If the original sender of an email was forged, these automated replies can be sent to uninvolved third parties. Some blocklists view this behavior negatively.

Additionally, certain verification mechanisms, such as sender callouts, can be considered suspicious by blocklist operators, even when legitimately used as part of an email security service.

For these reasons, Hornetsecurity IP addresses may be listed on UCEPROTECT.

Does Hornetsecurity Request Delisting from UCEPROTECT?

Hornetsecurity does not request paid removal of its IP addresses from UCEPROTECT.

Being listed does not automatically mean that spam was sent through Hornetsecurity. Hornetsecurity operates its own security mechanisms to detect and block harmful or abusive emails.

What Can You Do If Emails Are Rejected?

If emails are rejected due to a UCEPROTECT listing, the decision to block lies with the receiving mail server.

In this case, contact the recipient or their IT administrator. Ask them to review the configuration of the receiving mail server.

The recipient should not use UCEPROTECT as the sole criterion for rejecting emails. Alternatively, the recipient can whitelist the Hornetsecurity IP addresses to ensure legitimate emails continue to be delivered.

Note

The use of very restrictive blocklists can result in legitimate emails also being rejected. Hornetsecurity has no direct influence on which blocklists an external recipient uses for their mail server.