Email warm-up is designed to improve deliverability, but it does not guarantee instant inbox placement. Emails can still land in spam during warm-up if sending behavior triggers trust signals that email providers consider risky. Most spam placement during warm-up is not caused by content, it’s caused by behavior.
This article explains why spam placement happens during warm-up, what actions increase risk, and how to avoid common mistakes that can slow down or reverse reputation building.
Warm-up works by gradually introducing sending activity in a way that looks natural to email providers. However, providers continuously evaluate behavior in real time. If they detect inconsistencies, sudden changes, or conflicting activity, they may reduce trust—even during warm-up.
Spam placement during warm-up is usually a warning sign. It indicates that something in the sending pattern does not align with what providers expect for that account’s age or reputation.
Warm-up requires consistency and patience. Certain actions undermine the process and can quickly lead to spam placement.
Avoid sending large volumes outside the warm-up system, even if the emails are legitimate. Sudden increases in activity break the gradual trust-building pattern. Changing sending behavior too frequently, such as adjusting volume aggressively or switching sending modes repeatedly, can also confuse provider algorithms.
It’s equally important not to interfere with warm-up by deleting emails, disabling engagement actions, or modifying mailbox behavior in ways that reduce natural interaction signals.
Frequent pauses and restarts can negatively affect deliverability. When warm-up is stopped and restarted multiple times, email providers see irregular sending behavior. This can resemble automated or risky activity rather than steady human-like usage.
If a pause is necessary due to technical issues, it’s best to resume at a lower volume rather than immediately continuing from the previous level. Gradual re-entry helps rebuild consistency and reduces the risk of spam filtering.
Sudden volume increases are one of the most common reasons emails land in spam during warm-up. Even if the warm-up has been running smoothly, abrupt jumps in sending volume can signal abuse or automation.
Email providers expect volume to increase slowly and predictably. Large jumps—even after several days of clean warm-up- can trigger throttling, spam placement, or temporary restrictions. Consistent growth is safer than rapid scaling.
Running outreach or campaigns alongside warm-up is a major risk factor. When warm-up activity is combined with cold outreach, providers see conflicting sending patterns coming from the same mailbox or domain.
During the first two to three weeks of warm-up, it’s strongly recommended to avoid any parallel outreach. Cold emails introduce unknown recipients, low engagement, and potential spam signals that can override the positive signals warm-up is trying to build.
Even small outreach campaigns can negatively affect early warm-up stages.
Warm-up emails are designed to generate positive engagement signals such as replies and interactions. Outreach emails, especially cold ones, often produce low engagement or spam complaints. When these signals mix, providers may prioritize the negative signals.
This can result in:
Reduced inbox placement
Slower reputation growth
Warm-up interruptions
Increased spam filtering
Separating warm-up from outreach allows reputation to build cleanly.
If you notice spam placement during warm-up, avoid increasing volume or starting new campaigns. Allow sending behavior to stabilize and review recent changes. Common triggers include volume adjustments, pauses, or parallel sending activity.
In many cases, maintaining a steady warm-up pace and avoiding further changes allows inbox placement to recover naturally over time.
Warm-up is a process, not a switch. Emails can land in spam during warm-up if behavior conflicts with provider expectations. Most issues are caused by impatience, volume spikes, or mixing warm-up with outreach.
By keeping sending, avoiding parallel campaigns, and allowing warm-up to progress naturally, you give email providers the signals they need to trust your mailbox long term.