Why Some Warm-Up Emails Show as “Delivery Incomplete” or “Not Delivered”

While warming up your mailbox, you may notice some emails marked as “Delivery Incomplete” or “Message not delivered” in your email client. This can feel concerning, especially when your goal is to improve deliverability.

The good news is that this behavior is normal and expected during email warm-up. It does not mean the warm-up feature is broken or harming your mailbox.

Why Warm-Up Email Delivery Failures Happen

Email warm-up systems are designed to simulate real-world sending behavior. In real email environments, not every message is delivered successfully—and warm-up intentionally reflects that reality.

Common reasons warm-up emails may fail include:

• Invalid or unavailable recipient addresses

• Temporary server or email provider issues

• Mailbox or network restrictions on the receiving side

All warm-up services experience occasional delivery failures. These failures are a natural part of creating realistic sending patterns and do not negatively impact your warm-up progress or mailbox reputation.

Important Things to Know

• ❗ Delivery failures apply only to warm-up emails

• ✅ Your campaign emails and manually sent emails are not affected

• ✅ Warm-up continues working properly even if some messages fail

• ℹ Due to technical API limitations, failed warm-up deliveries cannot be displayed inside the platform

In short, seeing a few delivery failures does not mean your warm-up is failing.

If you ever have questions or want help reviewing your warm-up performance, our Customer Support team is always happy to help.