IP Warmup is the process of gradually increasing the volume of email sent from a new IP address to build up its reputation as a legitimate sender. This is important because when an IP address goes from sending no emails to sending a large volume, it can raise questions with the Internet Service Provider (ISP) and can cause the IP to be marked as Spam. By slowly ramping up the volume of email over a period of weeks or months, the IP can establish a good reputation with the ISP and avoid being flagged as Spam. This is especially important for businesses that rely on email marketing to reach their customers. IP Warmup can also help to ensure that emails are delivered to the Inbox, rather than being sent to Spam folders. When done correctly, IP Warmup is an essential part of any email marketing campaign.