Failing to properly warm up an IP address before sending email campaigns results in severe deliverability issues and a damaged sender reputation. Email providers view a sudden surge in email volume from a new IP address as suspicious, often flagging it as spam. This can lead to emails being filtered into the spam folder, blocked entirely, or the IP address being added to blocklists. A gradual warm-up is crucial to establish trust with ISPs and ensure emails reach the intended recipients. Real-world examples highlight instances where rapid warm-ups led to months of spam classification, underscoring the importance of following best practices.