Mailserver ip has a negative reputation but cannot be submitted for investigation

Hi,

a customer of me wants to send an email to someone, but the email cannot be delivered, because it's returning with the message that the mailserver ip is on the Symantec Global Bad Senders-List.
But if i want to submit the ip for investigation via http://ipremoval.sms.symantec.com/lookup/, it is said that the ip has no negative reputation.
But if i check the ip over http://www.symantec.com/security_response/landing/spam/, the reputation is bad.

The ip of the server is 62.75.186.48

So, what can i do now?

The mailserver is clearly not sending any spam and was checked multiple times.