Every email service provider (Google, Yahoo, etc.) assigns a reputation score to each sender’s IP address. Each sender is evaluated by how they follow best practices, such as promptly unsubscribing customers and high engagement, and by such things as customer-based spam complaints, message bounce rate, etc.
Therefore, if you are sending more than 50k emails per week, it can be a good idea to use a dedicated IP address in order to isolate your reputation from all the other senders. If you are sharing your IP with other senders, you are also sharing your reputation with those other senders.
The other thing for large volume senders to consider is using separate IPs for your bulk and transactional emails. These two types of email have very different engagement rates, so separating the two ensures that one does not impact the reputation of the other. Moreover, delivery of time-sensitive transactional emails may get queued behind a large batch of marketing emails, therefore separating these two may be a wise choice.
If you are interested in a dedicated IP (additional fees apply), contact CO-SENDER Support, we will be happy to help you with this.