Port 993: IMAPS

What is port 993 used for?

IMAP over TLS, the way email apps read mail securely.

Should port 993 be open?

Usually open to the internet. This port is meant to be reachable publicly on servers that offer the service. The standard incoming-mail port for most providers. Use it instead of 143.

See what is listening on port 993

# Linux
sudo ss -tlnp | grep ':993 '

# macOS
sudo lsof -nP -i TCP:993 -sTCP:LISTEN

# Windows (PowerShell)
Get-NetTCPConnection -LocalPort 993 -State Listen

Open or block port 993 in a firewall

# Ubuntu / Debian (ufw)
sudo ufw allow 993/tcp
sudo ufw deny 993/tcp

# Windows (PowerShell, as administrator)
New-NetFirewallRule -DisplayName "Port 993" -Direction Inbound -Protocol TCP -LocalPort 993 -Action Allow

On cloud servers, also open the port in the provider’s security group or network firewall. At home, a service behind a router needs a port-forwarding rule to the device’s local IP.

Test it from outside

A port can be open on the server but blocked upstream. The Port Checker connects from the internet, so it shows what the world sees. From your own machine, use nc -vz example.com 993 (macOS/Linux) or Test-NetConnection example.com -Port 993 (Windows).