SMTP Error 110 (Connection Timed Out): Causes and Fixes

Check if the SMTP server is reachable.

Run this command (Linux/Mac/Windows)

telnet mail.example.com 587

Expected response:

220 mail.example.com ESMTP Postfix

If you get "Connection timed out" or "Could not open connection":

• The server may be down or blocking SMTP connections.

If your SMTP server is self-hosted (Postfix/Exim), restart it:

sudo systemctl restart postfix    # For Postfix
sudo systemctl restart exim       # For Exim

Check logs:

sudo tail -f /var/log/mail.log      # Postfix logs
sudo tail -f /var/log/exim_mainlog  # Exim logs

Some ISPs block port 25. Try these instead:

• Port 587 > Recommended (STARTTLS)
• Port 465 > SSL/TLS
• Port 2525 > Alternative for some providers

Run this command to see if a firewall is blocking SMTP:

sudo iptables -L -n | grep 25

If you see DROP or REJECT, unblock SMTP:

sudo iptables -A OUTPUT -p tcp --dport 587 -j ACCEPT
sudo systemctl restart iptables

For Windows Firewall, allow outgoing SMTP:

1. Open Windows Defender Firewall.
2. Go to Advanced Settings > Outbound Rules.
3. Allow port 587 (or 465) for SMTP.

If using cloud hosting:

• Enable SMTP in security settings.
• AWS blocks port 25 by defau?????" request unblocking from AWS Support.

If your SMTP hostname (mail.example.com) is not resolving, clear DNS cache:

Windows

ipconfig /flushdns

Linux/macOS

sudo systemctl restart systemd-resolved

If your server is rejecting connections, check the logs:

Postfix Logs

sudo tail -f /var/log/mail.log

Exim Logs

sudo tail -f /var/log/exim_mainlog

Look for rate limiting or authentication failures.

If you have tried everything and SMTP still times out, contact your:

• Email hosting provider (e.g., Google, Microsoft, your mail host).
• Web hosting provider (if using cPanel, DirectAdmin, or VPS).
• ISP (if they block SMTP ports).