HTTPfy

Port 3905 (mupdate)

IANA assigns port 3905 to mupdate: Mailbox Update (MUPDATE) protocol.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
mupdate TCP Mailbox Update (MUPDATE) protocol - RFC 3656
mupdate UDP Mailbox Update (MUPDATE) protocol - RFC 3656

Check what is listening on port 3905

Linux: is anything listening on TCP 3905?
sudo ss -tlnp 'sport = :3905'
Linux: UDP 3905
sudo ss -ulnp 'sport = :3905'
Linux / macOS: which process owns the port
sudo lsof -nP -i :3905
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':3905 '
Windows (Command Prompt)
netstat -ano | findstr :3905
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 3905 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 3905
From Windows
Test-NetConnection HOST -Port 3905
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 3905

Block port 3905 in the firewall

ufw
sudo ufw deny 3905/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 3905 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 3905 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 3905' -Direction Inbound -Protocol TCP -LocalPort 3905 -Action Block
ufw
sudo ufw deny 3905/udp
iptables
sudo iptables -A INPUT -p udp --dport 3905 -j DROP
nftables
sudo nft add rule inet filter input udp dport 3905 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 3905' -Direction Inbound -Protocol UDP -LocalPort 3905 -Action Block

Related ports

3903charsetmgr3904omnilink-port3906topovista-data3907imoguia-port

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