Check result of IP
108.179.198.135

This is the rDNS found:

This IP was blocked by bad reputation in 50% of negative points.

In order for the IP to be removed from this list, the source MTA has to reduce the deliveries to customers who have complained, which have generated a SPFBL rejection prefix at the SMTP layer.

The reputation interval is seven days, so you should wait for this interval after all abuse has stopped.