IP Warmup and IP Reputation IP warming is the gradual process of establishing a reputation as a legitimate email sender in the eyes of ISPs (Internet Service Providers). When an ISP observes email suddenly coming from a new or “cold” (recently dormant) IP address, they will take notice and immediately begin evaluating the traffic coming from that IP. ISP spam filters look at volume as a significant factor when determining whether or not you are sending spam. Because of this, we recommend that you begin sending a low to moderate volume ( up to 1 million emails/month), eventually working your way up to larger volumes (over 1 million emails/month). This gives the receiving email providers a chance to closely observe your sending habits. In addition, the way your customers treat the emails they receive from you.