The number of emails you can send per dedicated IP before needing another isn't a fixed number, but rather depends on several factors. It's crucial to build and maintain a good sender reputation by sending consistent volume of engaging content to opted-in subscribers. Most experts agree on gradually warming up the IP by starting with small batches to highly engaged users and slowly increasing the volume. Monitor engagement metrics like open rates, bounces, and complaints, and adjust your sending practices accordingly. Considerations include the type of content, the target audience, and adherence to email best practices. Some rules of thumb suggest considering a second IP around 400k-500k emails per day, or at 2 million emails per day. However, it's more important to focus on the quality of your sending practices and your reputation.