Port 993 — IMAPS

TCP well-known

What runs on port 993

IMAP over TLS — the standard for mail clients.

Security considerations

Use this rather than 143.

Checking whether something is listening

# Linux / macOS — what is bound to the port
sudo lsof -i :993
sudo ss -lntp | grep :993

# Windows
netstat -ano | findstr :993
Get-NetTCPConnection -LocalPort 993

# is it reachable from outside?
nc -zv example.com 993
curl -v telnet://example.com:993

Freeing the port

# find the process, then stop it
sudo lsof -ti :993 | xargs kill        # Linux / macOS
netstat -ano | findstr :993            # note the PID, then:
taskkill /PID <pid> /F                    # Windows

Should this port be open to the internet?

Only on a mail server. If this port is open on something that is not intentionally handling mail, you may be running an open relay — which will get the IP blacklisted quickly.

Quick reference

Frequently asked questions

Other common ports

• Port 20 — FTP data
• Port 21 — FTP control
• Port 22 — SSH / SFTP
• Port 23 — Telnet
• Port 25 — SMTP
• Port 53 — DNS
• Port 67 — DHCP server
• Port 68 — DHCP client
• Port 69 — TFTP
• Port 80 — HTTP
• Port 110 — POP3
• Port 123 — NTP
• Port 143 — IMAP
• Port 161 — SNMP
• Port 389 — LDAP
• Port 443 — HTTPS
• Port 445 — SMB
• Port 465 — SMTPS

All port numbers