"Snow shoe spamming" false positive

We have an uncompromised mailserver with four IPs:

- 212.129.48.30
- 212.129.48.31
- 212.129.48.32
- 212.129.48.33

IP lookup on the Symantec page shows that this four IPs have a negative reputation: "The host has been observed sending spam in a format that is similar to snow shoe spamming techniques".

This is a recurring problem.
I assume your system confuses some notifications sent from the server with this spam technique.

Our IPs is not listed on any other blacklists (very good reputation on SenderScore), and the server have been scanned thoroughly and are clean.

Please let me know what we can do to clear the reputation for our IP permanently.

Regards,
Thibault