📬 Overview

If Mailbird tells you that your SMTP server rejected the connection because your IP is blacklisted (or shows response codes like OB115, OB119, or mentions Abusix, Cloudmark, or a "blocklist"), the mail server you're trying to send through has flagged the IP address your connection is coming from as suspicious.

This is not caused by Mailbird or your email credentials — it's a network-level block.

🔍 Why does this happen?

SMTP servers use IP reputation databases (Spamhaus, Abusix Mail Intelligence, Cloudmark, SORBS, and others) to reject connections from IPs that have sent spam or abusive traffic. Your IP can appear on these lists for reasons completely unrelated to you, for example:

• Your internet provider assigned you a shared or dynamic IP that was previously used by a spammer.
• Another device on your network (e.g. a compromised computer, printer, or IoT device) is sending spam.
• You're on a VPN whose exit IP has been flagged.
• Your office or campus network uses a shared NAT gateway that has been flagged.

🛠️ How to fix it

1. Try a different network

This is the fastest way to confirm the issue is IP-based:

• Switch to a different Wi-Fi network (home vs. office, or a coffee shop).
• Use your phone's mobile hotspot.
• If Mailbird connects successfully on a different network, the original IP is the problem.

2. Disable your VPN

If you're using a VPN, disconnect it and try again. Shared VPN exit IPs are frequently flagged.

3. Restart your router

If your ISP uses dynamic IPs (most home connections), restarting your router usually assigns a new IP:

1. Unplug your router for 2-3 minutes.
2. Plug it back in and wait for the connection to restore.
3. Check your new public IP at whatismyip.com.
4. Try sending an email again.

4. Check if your IP is listed

Look up your public IP on blocklist checkers to confirm:

• MXToolbox Blacklist Check
• Abusix Mail Intelligence Lookup

If your IP is listed, each list has a delisting request form. Instructions vary by provider.

5. Contact your ISP

If your IP keeps getting flagged, your internet provider can investigate whether the block applies to a range of addresses, and may be able to assign you a clean IP.

6. Scan your network for compromised devices

If a device on your network is sending spam, fixing that will let your IP get delisted. Look for:

• Computers showing high outbound traffic when idle.
• IoT devices (smart TVs, cameras, printers) with outdated firmware.
• Unknown devices connected to your Wi-Fi.

💬 Need more help?

If you've tried the steps above and your IP is still being blocked, contact our Customer Happiness Team. Include a screenshot of the full error message — the specific blocklist code (OB115, OB119, etc.) helps us identify the right next step.