If you’ve ever noticed that some of your emails take longer to reach recipients, or occasionally don’t appear at all, greylisting may be the reason. Understanding this email filtering mechanism is important for anyone running newsletters or marketing campaigns.

In this post, we’ll explain what greylisting is, how it works, and what you can do to ensure your emails reach subscribers reliably.

What Is Greylisting?

Greylisting is an anti-spam technique used by email servers to temporarily reject incoming messages from unknown senders. When a server receives an email from a sender it doesn’t recognize, it returns a temporary error, asking the sending server to try again later.

Legitimate email servers automatically retry sending the message after a short delay, while many spam servers give up. This helps reduce unwanted spam without requiring complex content analysis.

How Greylisting Works

Here’s the typical process:

1. Your email is sent to a recipient’s server.
2. The server doesn’t recognize your sending domain or IP address and temporarily rejects the email.
3. Your email server retries sending the message after a delay (usually a few minutes to an hour).
4. The recipient’s server accepts the email on the retry.

From the recipient’s perspective, the email eventually arrives, but it may be delayed compared to other messages.

How Greylisting Can Affect Newsletter Delivery

While greylisting is useful for blocking spam, it can impact email newsletters in several ways:

• Delayed Delivery: Your email may not appear in inboxes immediately. For time-sensitive campaigns like flash sales or event reminders, this can reduce effectiveness.
• Initial Bounce Notifications: If you’re sending from a new IP address or domain, you might temporarily see bounce notifications until the server accepts your retry.
• Reputation Sensitivity: Frequent delays or failed retries can affect your sender reputation over time, especially if your email server isn’t configured correctly.

It’s important to understand that greylisting doesn’t mean your email is blocked permanently — it just slows delivery until the sending server proves it’s legitimate.

How to Minimise the Impact of Greylisting

Here are practical steps to reduce delays caused by greylisting:

1. Use a Reputable Email Sending Service
   Email platforms like Email Blaster have dedicated, properly configured servers that comply with best practices. These servers are less likely to be delayed by greylisting.
2. Authenticate Your Emails
   Implement SPF, DKIM, and DMARC records. These authentication protocols verify your sending domain and build trust with recipient servers, reducing the chance of greylisting delays.
3. Maintain a Consistent Sending IP
   Avoid frequently changing the IP address from which your emails are sent. Servers recognize consistent IPs as legitimate senders, speeding up acceptance.
4. Warm Up New Domains or IPs
   If you’re using a new domain or IP for email marketing, gradually increase sending volume. This builds trust with recipient servers and reduces the likelihood of greylisting delays.

Final Thoughts

Greylisting is a common and effective tool used by email servers to combat spam. While it can delay email delivery, it’s not a permanent barrier — and with proper setup, you can minimise its impact.

At Email Blaster, our platform ensures your newsletters are sent from trusted, authenticated servers, maximising deliverability and reducing the risk of greylisting delays. By following best practices for email authentication and sending consistency, your campaigns will reach subscribers reliably and on time.