What causes emails to go to spam when migrating to a new ESP and warming an IP?

When migrating email sending to a new Email Service Provider (ESP) and warming a new IP address, emails frequently land in spam folders due to a combination of factors. New IP addresses lack an established sending history, making them inherently suspicious to Internet Service Providers (ISPs), who often throttle or block unproven senders. Sending too much volume too quickly, or with inconsistent patterns, signals risky behavior and rapidly damages the nascent IP reputation. Furthermore, improper configuration of crucial DNS authentication records like SPF, DKIM, and DMARC for the new ESP's infrastructure prevents ISPs from verifying sender legitimacy, leading to immediate spam filtering. High bounce rates, spam complaints, and low engagement from uncleaned or unengaged lists are also significant contributors, as these negative signals indicate poor list hygiene and sender practices, negatively impacting the new IP's deliverability. The domain's existing reputation and content quality also play a role, requiring senders to meet higher standards of engagement and data quality when transitioning to ensure inbox placement.

When transitioning email sending to a new ESP and initiating IP warming, several common pitfalls can lead to emails being delivered to spam folders. A primary issue is the inherent lack of trust associated with new IP addresses, which have no established sending history and are often viewed cautiously by Internet Service Providers (ISPs). Attempting to send high volumes too rapidly on a new IP mimics spammer behavior, triggering immediate suspicion and leading to throttling or blocking. Furthermore, if critical DNS authentication records like SPF, DKIM, and DMARC are not accurately configured for the new sending infrastructure, emails will fail authentication checks, preventing ISPs from verifying the sender's legitimacy. Another significant factor is the quality of the email list; sending to unengaged, outdated, or poorly opted-in subscribers results in elevated bounce rates and spam complaints. These negative engagement signals, along with hitting spam traps, severely damage the new IP's nascent reputation. Moreover, the existing reputation of the sender's domain, along with content quality and adherence to ISP feedback loops, continue to play a vital role, as issues in these areas can override successful IP warming efforts.

During the crucial period of migrating to a new Email Service Provider and warming a new IP address, emails frequently encounter spam filtering because recipient Internet Service Providers (ISPs) and their filters are actively observing and learning from user interactions. Without prior established sending history, new IP and domain combinations inherently appear less trustworthy, even when sending to the same subscriber base. This lack of historical data prompts filters to initially deliver messages in a mix of inbox and spam, assessing how recipients engage. Consequently, senders must elevate their email practices, demanding a higher standard of data quality, relevance, and user engagement, as simply replicating past behaviors is insufficient. The rapid escalation of email volume from a cold IP further reinforces ISP caution, underscoring the critical need for a gradual warming process and proactive external communication to subscribers.

When migrating to a new Email Service Provider and warming an IP address, emails frequently land in spam folders due to a confluence of factors, primarily stemming from Internet Service Providers' (ISPs) inherent caution with new sending origins. ISPs rigorously monitor for consistent sending volumes, as well as complaint and bounce rates; any deviation or rapid increase signals poor sender practices, swiftly eroding the new IP's reputation. Crucially, incomplete or incorrect DMARC, SPF, and DKIM authentication records for the new ESP's domains prevent ISPs from verifying sender identity, often resulting in immediate spam filtering. Furthermore, recipient feedback, particularly high spam complaints and low engagement, significantly influences sender reputation, quickly flagging a new IP regardless of technical setup, indicating potential list quality issues or inappropriate sending during the critical warming period.