Using a dedicated IP address is one of the most effective, yet least used, tactics to improve deliverability. Because your deliverability is only as strong as your weakest sender, your mailing reputation and deliverability is at the mercy of other marketers. Can you imagine handing the keys to your marketing program over to a complete stranger? Me neither! That’s why I recommend using a dedicated IP address whenever possible.
However, it’s a good point to bring up that there are some instances where using a shared IP address may actually work in your favor. Here’s how:
THEN you may want to consider using a shared IP address. The benefits in this case is that you have a less volatile complaint rate, and ISPs and e-mail providers have an easier time assigning a reputation to higher volume mailers.