ポート 993 — IMAPS (TCP)
What is Port 993?
セキュアIMAP
This is a well-known port (0–1023) commonly used by core services like IMAPS. · RFC 9051
When do you need Port 993 open?
Open on mail servers to let clients access email over encrypted IMAP. Preferred over plain IMAP (port 143). Required if you run a mail server and want mail apps to connect securely.
Common uses and software
- Microsoft Outlook
- Mozilla Thunderbird
- Apple Mail
- Gmail
- Fastmail
- Proton Mail Bridge
Security
IMAPS is the secure standard for IMAP access. Ensure TLS 1.2 or higher and a valid, non-expired certificate. Disable the plain-text IMAP port (143) to prevent accidental unencrypted connections. Monitor failed authentication attempts as they may indicate password spraying.
Is Port 993 safe?
An open port increases your attack surface. Safety depends on how IMAPS is configured.
Keep IMAPS up to date with security patches. Require strong authentication and restrict access to the minimum necessary IP addresses.
Test connectivity for Port 993 on any host.
How to Open Port 993
To allow incoming connections to Port 993 (IMAPS) 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: 993 → Allow the connection → Name and save the rule.
netsh advfirewall firewall add rule name="Open Port 993" dir=in action=allow protocol=tcp localport=993sudo ufw allow 993/tcpsudo iptables -A INPUT -p tcp --dport 993 -j ACCEPTLog into your router (192.168.1.1 or 192.168.0.1) → Port Forwarding → Add a new rule: Protocol TCP, External port 993, Internal IP: your device's local IP, Internal port 993 → Save.
How to close Port 993
If you do not need IMAPS, block this port in your firewall or router.
To block port 993 on Windows, run the following command in PowerShell or Command Prompt (as Administrator):
netsh advfirewall firewall add rule name="Block Port 993" dir=in action=block protocol=tcp localport=993sudo ufw deny 993/tcpsudo iptables -A INPUT -p tcp --dport 993 -j DROPRemove or disable any port forwarding rule for Port 993.
Frequently Asked Questions
What is Port 993 used for?▾
Port 993 is the default TCP port for IMAPS. 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 IMAPS server — if not, it should remain closed to reduce your attack surface.
Is Port 993 safe to keep open?▾
An open Port 993 increases your attack surface. If you are not actively running IMAPS, close this port in your firewall and remove any port forwarding rules. If IMAPS must be accessible, restrict access to known IP ranges, keep the service software updated with security patches, and use strong authentication.