Bad reputation IP

Hi, for some reason our servers from 167.114.4.104-107 are getting blocked by the email service and no emails are being delivered.

None of the IPs are listed on any other blacklist so I wonder if this is a false positive. All emails are legitimate email servers.

This is the error I get: 

• The host has been observed sending spam in a format that is similar to snow shoe spamming techniques.

How can I get them removed permanently?

I remove them and they get listed again.

Thanks much in advance,

Teo