Using Express ‘Em, the use of private or dedicated sending IP’s are crucial the more you send. For every 250,000 1 free IP is provided for sending, for instance, 1,000,000 offers 4 free dedicated sending IP’s. Check out this awesome article “Shared vs Dedicated Sending.”
There are twp types of IP’s when it comes to email marketing.
Pre-warmed IP: Warming up your IP allows you to gradually send more emails over your new IP to establish a good sender reputation. All IP’s have at one point have started as a cold IP (no reputation) and need work to build sending reputation up. Pre-warmed IP’s have already completed the warming stage and are ready for higher volume.
When an ISP observes email suddenly coming from a new or “cold” IP address, they will take notice and immediately begin evaluating the traffic coming from that IP. Since ISPs treat email volume as a key determining factor when detecting spam, it is best to begin sending a low to moderate volume, eventually working your way up to larger volumes when using new dedicated IP’s. This gives the receiving email providers a chance to closely observe your sending habits and record how your recipients engage with your email.
Pre-warmed IP’s are $24.99 per month and New Dedicated (COLD) IP’s are $7.95 per month (require warming before high volume sending).
Check out this awesome article “How to warm your dedicated IP“.