How to Monitor Email Deliverability During Warm-Up

When launching emails from a new domain or migrating to a new ESP, you’re probably eager to hit send and get your campaigns rolling. But if you jump in too fast, your emails might never make it to the inbox — or worse, they could end up in spam.

The early days of sending emails from a new domain are critical. This is when inbox providers are watching closely to determine whether you’re a legitimate sender or a potential spammer. That’s why domain warm-up and its monitoring isn’t just a technical formality, it’s a high-stakes trust-building phase.

In this guide, we’ll walk you through how to track and monitor your email deliverability using Mailmodo during the warm-up process — so you avoid pitfalls, protect your sender reputation, and ensure your messages land exactly where they’re meant to.

What is email warm-up and why does it matter?

Email warm-up is the process of gradually increasing the volume of emails sent from a new domain or IP address to build a positive sender reputation with inbox providers like Gmail, Outlook, and Yahoo.

Much like building credit, sending emails from a new domain is all about establishing consistent, responsible behavior over time. If you try to send to a large list immediately, ISPs will likely treat your domain as suspicious — leading to low inbox placement or outright blocking.

A proper warm-up strategy tells inbox providers that:

• You send relevant, expected emails

• You care about engagement and quality

• You're not a spammer blasting out bulk messages from a cold domain

But warming up is only one side of the equation. The other — equally important — part is monitoring how your emails perform as you warm up.

Why monitoring deliverability is critical during warm-up

Deliverability isn’t just about sending emails — it’s about where those emails land. If they’re not landing in the inbox, your entire strategy is at risk.

Monitoring during warm-up helps you:

• Catch early signs of trouble, like low open rates or high spam complaints

• Understand how mailbox providers perceive your domain

• Adjust sending behavior before minor issues become major reputation problems

Without monitoring, you’re flying blind. You could be landing in spam and not even know it until it’s too late. That’s why real-time visibility into deliverability signals is non-negotiable during this phase.

How to monitor deliverability during warm-up

Mailmodo doesn’t just help you warm up your domain, it also gives you clear visibility into how your deliverability is performing throughout the process. You can track key engagement and reputation metrics directly within the platform. Here’s how you can keep a check on your domain’s health during warm-up.

1. Use the campaign metrics dashboard

Your first stop for deliverability insights is Mailmodo’s Campaign Metrics Dashboard. This dashboard offers real-time visibility into how your emails are performing across several key metrics:

Metrics to monitor:

• Open rates: A strong indicator of inbox placement. If your open rates are consistently low, your emails may be going to spam or promotions.

• Click rates: Clicks reflect actual engagement and signal value to inbox providers. A healthy click rate helps reinforce trust.

• Spam complaints: Arguably the most damaging metric. Even a few complaints can hurt your sender reputation. Monitor this closely.

In Mailmodo, filter your metrics by specific campaign batches or time ranges to identify trends. If you notice a drop in open rates or a spike in spam complaints, adjust your sending volume or rethink your warm-up strategy.

You need monitor these metrics frequently during the first few weeks, as small signals often indicate potential inboxing issues before they escalate.

2. Track your domain reputation score

Beyond engagement metrics, Mailmodo gives you direct visibility into your domain’s health.

Your sender domain’s reputation is categorized as:

• High

• Medium

• Low

These categories reflect how mailbox providers currently view your domain based on your recent sending behavior and recipient engagement.

You should check your reputation score daily during the warm-up phase. If your score drops from high to medium or from medium to low, investigate potential issues in your campaigns, such as increased complaints, low engagement, or poor list quality. Avoid increasing your sending volume while your domain reputation is unstable or trending downward.

3. Check bounce rates to catch list issues early

While bounce rates don’t directly determine inbox placement, they’re still an important deliverability signal — especially during warm-up. Monitoring them helps you identify problems with your email list early on, before they escalate into bigger reputation issues.

Bounces are categorized into:

• Hard bounces: They occur when an email address is invalid or non-existent

• Soft bounces: They are temporary failures that happens due to full inboxes or server-side issues

During the warm-up phase, you’re sending to a smaller and more engaged segment, so bounce rates may not have a big impact right away. But that’s exactly why it’s the ideal time to catch and fix list quality issues. Cleaning up bad addresses early helps prevent reputation damage when you scale up volume later.

By tracking bounce rates throughout your warm-up campaigns, you ensure your list stays healthy and you’re not carrying over hidden risks into your high-volume sends.

Conclusion

Deliverability monitoring during the warm-up process isn’t just a technical task — it’s a critical safeguard for your email program. When you're building trust with inbox providers, every signal counts. Monitoring performance in real time helps you identify issues early, understand how mailbox providers perceive your domain, and adjust your approach before problems escalate. With the right tools and visibility, you can navigate the warm-up period with confidence and set the stage for long-term inbox success.