🌐 Overview

This article covers a group of network-related errors in Mailbird Next that prevent the app from reaching your email server. These errors are typically caused by DNS resolution failures, blocked connections, or incorrect server addresses.

⚠️ Error References

The following errors indicate network connectivity problems:

• Error #14 — DNS resolution failed (the server hostname could not be found)
• Error #15 — Connection refused by the remote server
• Error #16 — Connection to localhost or loopback address (server address is misconfigured)
• Error #18 — Address unavailable or unreachable
• Error #39 — General network connectivity failure

🔍 Common Causes

• Incorrect server hostname — A typo in the IMAP, POP3, SMTP, or Exchange server address.
• DNS issues — Your network’s DNS server cannot resolve the mail server’s hostname.
• Server is down — The mail server is temporarily unavailable.
• Firewall or network restrictions — A firewall, proxy, or corporate network is blocking the connection.
• Localhost/loopback address — The server address has been set to 127.0.0.1 or localhost by mistake.
• VPN interference — A VPN may be routing traffic incorrectly.

🛠️ How to Fix It

1. Verify Your Server Settings

Double-check the server addresses in your account settings:

1. Click the Settings icon (gear) in the bottom-left corner of Mailbird Next.
2. Go to Accounts and select the affected account.
3. Verify the incoming and outgoing server hostnames are correct.

Common correct formats:

• IMAP: imap.yourdomain.com (port 993)
• SMTP: smtp.yourdomain.com (port 587)
• Exchange: https://mail.yourdomain.com/EWS/Exchange.asmx

Make sure the address is not set to localhost, 127.0.0.1, or any other local address.

2. Test DNS Resolution

Open Terminal on your computer and run:

nslookup imap.yourdomain.com

If this returns an error or no address, your DNS is not resolving the hostname. Try:

• Switching to a public DNS server (e.g., 8.8.8.8 for Google DNS or 1.1.1.1 for Cloudflare).
• Flushing your DNS cache: sudo dscacheutil -flushcache; sudo killall -HUP mDNSResponder

3. Check If the Server Is Reachable

In Terminal, test connectivity:

nc -zv imap.yourdomain.com 993

If the connection is refused or times out, the server may be down or a firewall may be blocking the port.

4. Disable VPN or Proxy Temporarily

If you’re using a VPN or proxy, try disconnecting it temporarily to see if the issue resolves.

5. Check Firewall Settings

Ensure your macOS firewall and any third-party security software are not blocking Mailbird Next. See our Antivirus or Firewall Blocking Mailbird Next article for detailed steps.

6. Try a Different Network

If possible, connect to a different Wi-Fi network or use a mobile hotspot to rule out network-specific issues.

💬 Need More Help?

If you’ve tried the steps above and are still seeing network errors, please contact our Customer Happiness Team. We’re always here to help.