Port 993 (IMAPS)

IMAP over implicit TLS, the standard port for mail clients reading mail.

Well-known (system) port, 0-1023 TCP Email Meant to face the internet

What port 993 is used for

IMAP over implicit TLS, the standard port for mail clients reading mail.

Security: should port 993 be open?

Meant to face the internet. Fine to expose on a mail server. Expect password-spraying; use MFA or app passwords where possible and monitor failed logins.

IANA assignment

Service nameProtoDescriptionAssigneeReference

imaps TCP IMAP over TLS protocol IESG RFC 3501, RFC 8314, RFC 9051

Registry dates for this port: last modified 2021-02-22.

Check what is listening on port 993

Linux: is anything listening on TCP 993?

sudo ss -tlnp 'sport = :993'

Linux / macOS: which process owns the port

sudo lsof -nP -i :993

Older Linux / BSD (net-tools)

sudo netstat -tlnp | grep ':993 '

Windows (Command Prompt)

netstat -ano | findstr :993

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 993 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine

nc -vz -w 5 HOST 993

From Windows

Test-NetConnection HOST -Port 993

Open port 993 in the firewall

ufw

sudo ufw allow 993/tcp

iptables

sudo iptables -A INPUT -p tcp --dport 993 -j ACCEPT

nftables

sudo nft add rule inet filter input tcp dport 993 accept

Windows Firewall

New-NetFirewallRule -DisplayName 'Allow TCP 993' -Direction Inbound -Protocol TCP -LocalPort 993 -Action Allow

All port numbers · Open port checker
Assignment data: IANA port number registry (public domain), retrieved 2026-11-10.