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Port 5757 (x500ms)

IANA assigns port 5757 to x500ms: OpenMail X.500 Directory Server.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
x500ms TCP OpenMail X.500 Directory Server OpenMail Encyclopedi, Don Loughry -
x500ms UDP OpenMail X.500 Directory Server OpenMail Encyclopedi, Don Loughry -

Check what is listening on port 5757

Linux: is anything listening on TCP 5757?
sudo ss -tlnp 'sport = :5757'
Linux: UDP 5757
sudo ss -ulnp 'sport = :5757'
Linux / macOS: which process owns the port
sudo lsof -nP -i :5757
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':5757 '
Windows (Command Prompt)
netstat -ano | findstr :5757
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 5757 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 5757
From Windows
Test-NetConnection HOST -Port 5757
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 5757

Block port 5757 in the firewall

ufw
sudo ufw deny 5757/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 5757 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 5757 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 5757' -Direction Inbound -Protocol TCP -LocalPort 5757 -Action Block
ufw
sudo ufw deny 5757/udp
iptables
sudo iptables -A INPUT -p udp --dport 5757 -j DROP
nftables
sudo nft add rule inet filter input udp dport 5757 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 5757' -Direction Inbound -Protocol UDP -LocalPort 5757 -Action Block

Related ports

5750rscd5755openmailg5766openmailns5767s-openmail

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