Port 143 — IMAP (TCP)
What is Port 143?
IMAP per il recupero delle email.
This is a well-known port (0–1023) commonly used by core services like IMAP. · RFC 9051
When do you need Port 143 open?
Open on mail servers where email clients sync messages via IMAP. Prefer IMAPS (port 993) for encrypted connections. Not needed if you are not hosting a mail server.
Common uses and software
- Microsoft Outlook
- Mozilla Thunderbird
- Apple Mail
- Gmail IMAP bridge
- Fastmail
- Proton Mail Bridge
Security
Plain IMAP sends authentication tokens and email content unencrypted. Enable STARTTLS at minimum on port 143. Better: disable port 143 entirely and use IMAPS (port 993) only. This prevents client misconfiguration from accidentally connecting without encryption.
Is Port 143 safe?
An open port increases your attack surface. Safety depends on how IMAP is configured.
Keep IMAP up to date with security patches. Require strong authentication and restrict access to the minimum necessary IP addresses.
Test connectivity for Port 143 on any host.
How to Open Port 143
To allow incoming connections to Port 143 (IMAP) from outside your network, configure your firewall and add a port forwarding rule on your router pointing to your device's local IP address.
Open Windows Defender Firewall → Advanced Settings → Inbound Rules → New Rule → Port → TCP → Specific local ports: 143 → Allow the connection → Name and save the rule.
netsh advfirewall firewall add rule name="Open Port 143" dir=in action=allow protocol=tcp localport=143sudo ufw allow 143/tcpsudo iptables -A INPUT -p tcp --dport 143 -j ACCEPTLog into your router (192.168.1.1 or 192.168.0.1) → Port Forwarding → Add a new rule: Protocol TCP, External port 143, Internal IP: your device's local IP, Internal port 143 → Save.
How to close Port 143
If you do not need IMAP, block this port in your firewall or router.
To block port 143 on Windows, run the following command in PowerShell or Command Prompt (as Administrator):
netsh advfirewall firewall add rule name="Block Port 143" dir=in action=block protocol=tcp localport=143sudo ufw deny 143/tcpsudo iptables -A INPUT -p tcp --dport 143 -j DROPRemove or disable any port forwarding rule for Port 143.
Frequently Asked Questions
What is Port 143 used for?▾
Port 143 is the default TCP port for IMAP. It is used by servers and applications that need to accept incoming connections for this service. Whether you need it open depends on whether you are actively running a IMAP server — if not, it should remain closed to reduce your attack surface.
Is Port 143 safe to keep open?▾
An open Port 143 increases your attack surface. If you are not actively running IMAP, close this port in your firewall and remove any port forwarding rules. If IMAP must be accessible, restrict access to known IP ranges, keep the service software updated with security patches, and use strong authentication.